With the current emphasis on electrification and decarbonization coming from local, State and Federal bureaucracies, there is a lot of talk about using heat pumps to displace fossil fuel appliances and low-efficiency standard AC condensers. Of course, heat pumps have been around for a long time in the HVAC industry. When discussing heat pumps, historically there have been three categories:
• Air-to-Air heat pumps
• Water-to-Air heat pumps
• Water-to-Water heat pumps
In general, heat pumps are devices that can convert low-temperature heat into higher-temperature heat. The low-temperature medium is referred to as the source. This is where the energy comes from to heat the building. The “source” can be the outdoor air or tubing buried in the ground. This is where the “free” heat comes from—the renewable energy source. The converted “higher temperature” energy is then released into the sink—the place that can absorb this energy. An example would be an air handler unit that is moving cooler return air across a coil (the heat exchanger) and delivering the warmer air into the living space.
Most are familiar with Air-to-Air heat pumps, especially the mini-split units. They extract heat from the outside air and are very common throughout our market. Air-to-Air heat pumps deliver the high-temperature heat through either a forced-air network of duct throughout a home, or individual cassettes mounted throughout various rooms in the house. This type of heat pump is classified as an air-source heat pump. There are other heat pumps that extract heat by using water that is circulated through tubing that is buried in the ground. The earth heats the water circulating through a “field” of tubing and this heat is then converted by the heat pump into a higher temperature medium. If it is air, they are known as Water-to-Air heat pumps and if the high-temperature medium is water, then they are referred to as Water-to-Water heat pumps.
There is one additional type of heat pump that is starting to gain attention in our industry called an Air-to-Water heat pump. This style is similar to wall-hung boilers and can produce water temperatures from around 85°F up to 130°F. Air-to-Water heat pumps do not burn fossil fuel, which is another reason they are gaining in popularity. This unit extracts heat from the ambient air outside the home and transfers it through refrigerant piping to a module. This module contains a refrigerant-to-water plate heat exchanger that heats water, which is then circulated through floor heating systems, fan coils and low-temperature radiators. Since it is a heat pump, the whole cycle can be reversed and provide chilled water (45°F) for cooling. Air-to-Water heat pumps have been gaining popularity in Europe for the last 10–15 years.
Why a Heat Pump?
Heat pumps are considered the most energy efficient, electrically-operated heating and cooling system on the market. These modern Air-to-Water heat pumps can deliver between 3–5kWh of usable heat for every 1kWh of electricity that it uses. This equates to a Coefficient of Performance (COP) of 3–5 or 300%–500% more efficient than typical electrical resistance heat. The heat pump uses the renewable energy source (air) and therefore has no localized CO2 emissions. The same system can be used for heating in the Winter and cooling in the Summer. Another benefit to this style of heat pump is that they use an inverter technology to operate the compressor and can vary the speed of the compressor to match the actual load that the system is currently experiencing. This can provide more comfort by matching the output to the load. Furthermore, cycle losses are reduced, which increases the compressor’s efficiency and reduces wear and tear on the compressor, thus extending its life cycle.
By using air instead of geothermal energy, one can eliminate the expenses associated with drilling a well field and installing the tubing (anywhere from $10,000–$30,000), consuming the necessary footprint to support the well field and the operating costs of pumping the well all year long.
Where Does the Heat Come From?
Generally speaking, the heat contained in the soil, ground water and air all started as solar energy. Basically, we are taking energy from the sun and using it to heat the water for the hydronic systems. During warmer weather, the ground and the air absorb this heat and, as the weather gets colder, some of this heat dissipates to the outside air. However, the heat absorbed into the soil can take a long time to transfer back to the atmosphere—so even in the middle of Winter, the soil temperature in the earth is much warmer than the outside air temperature. This condition generally favors water source heat pumps because their efficiency or thermal performance remains high due to the warmer-source water temperature, whereas an Air-to-Water heat pump’s output capacity drops as the outside air temperature gets very cold (0°F to 25°F). The manufacturers are continuing to try and improve the efficiency of the refrigerant cycle, enabling the units to extract heat from colder temperatures while maintaining their capacities.
How the Heat Pump Does What It Does
Refrigerant plays a major role in the successful transfer of energy from one place where it is available to another place that needs or wants it. The refrigerant is a chemical that has unique properties that allow it to absorb heat from low temperatures and transfer that energy to a medium operating at higher temperatures. For this to happen, the refrigerant has to change its state from liquid to vapor and then back to liquid—and in doing so, undergo some pressure changes.
This whole process can be referred to as the “Refrigeration Cycle” and is the starting point for the operation of all vapor-compression heat pumps. There are four components that play a major role in this cycle. Their respective names indicate their function and how they play their part in the process:
• Evaporator
• Compressor
• Condenser
• Thermal expansion valve
First, a cold liquid refrigerant enters into the evaporator. The pressure of this cold liquid 410A refrigerant is low, and there is a direct relationship between the pressure that the refrigerant is at and what its corresponding temperature is, so that the lower the pressure, the lower the refrigerant’s temperature. Additionally, the refrigerant’s pressure/temperature will adjust as the “source” (air) temperature changes. As it gets colder outside, the temperature of the liquid has to become colder so that it can absorb heat from the relatively cold air outside. The key is, as it absorbs heat from the air outside, the refrigerant evaporates or changes state into a vapor or gas. Its temperature is still low, but warmer than when it was a liquid. This step is important because the next component in the system is the compressor and since liquids aren’t compressible, if the refrigerant didn’t evaporate into a vapor, the liquid entering the compressor would severely damage it.
The compressor’s job is just as it sounds: it compresses the low-temperature vapor. This creates a large increase in both its pressure as well as its corresponding temperature as the refrigerant leaves the compressor. Another factor to consider is that the electrical energy used to compress the refrigerant by the compressor is added to the refrigerant. Now we have a high-temperature vapor that contains a lot of energy ready to be utilized.
This high-pressure, high-temperature vapor then enters the condenser, and the cooler return water from the hydronic system is pumped across the exchanger. The refrigerant, being hotter than the water, transfers its energy to the cooler water, elevating the water temperature going back out to the heating system. This transfer of energy causes the refrigerant to change its state and condense back to a high-pressure liquid.
The last step in this process is for the high-pressure/high-temperature liquid refrigerant to flow through an expansion valve (either thermal or electronic). The expansion valve controls the flow of the liquid refrigerant through its orifice, drastically reducing its pressure and thus its temperature so that the refrigerant is back to the cold temperature it was at the beginning of this process. As Air-to-Water Heat Pumps become more popular, they will find a place in the renewable energy industry.
If you have any questions or comments, e-mail me at [email protected], call me at (800) 423-7187 or follow me on Twitter at @Ask_Gcarey. ICM
As this column is being written for publication, we have been experiencing a very strange Winter in the Northeast area with some fairly wild temperature swings. One weekend in February, it was -12°F in Gloucester, MA, on Saturday morning and by Sunday, the temperature had climbed to 45°F. All the while, heat is still required and heating systems need to operate to maintain certain indoor air temperatures regardless of the outdoor temperature.
One of those systems was an older steam system that experienced banging noises whenever the thermostat called for heat. It all started when the old boiler finally quit. The replacement boiler was considerably smaller physically and consequently held less water. This created the need to install a boiler feed tank, which acted as a reservoir for the new replacement boiler and helped prevent the boiler from shutting down due to low water conditions (or flooding the boiler if a water feeder is present). This occurred when the automatic feeder became overactive due to the lack of water in the replacement boiler. With the boiler feed tank, all the system surges took place in the receiver, allowing the boiler to maintain a steady water line. This by itself isn’t uncommon, but trying to install the new boiler feed unit into these older systems can be treacherous and expensive if you are not careful—especially considering that the original system was not intended to have a vented receiver attached to it.
This particular system was a two-pipe air vent system. Due to its age, these systems were installed when one-pipe steam would have been the popular method of heating. In fact, at the time, steam traps hadn’t yet been invented. The heat loss in large, old buildings was great, which called for extremely large radiators. It was also very common to bring in outside air to ventilate the building; this was accomplished with large indirect radiators located inside tin ductwork.
In one-pipe steam systems, the riser, which supplies the steam, also handles the condensate that forms in the radiation. There is a counter-flow action that takes place inside those pipes. For this reason, it was important to have the right size pipe to handle those large loads. If the pipe was too small, it would cause spitting radiator vents and water hammer. To prevent this, heating engineers had to use “sewer-like” pipe sizes and supply valves to handle the condensate that would form by these large radiators. Another option was to use a second pipe on the outlet side of the radiator to handle the condensate, thus eliminating the counter-flow problem. The system could be described as a one-pipe/ two-pipe system because each radiator still used a steam vent. However, engineers had to ensure that the return pipe drained down individually to a wet return. This was important because the water acted like a trap, preventing steam from passing into the return side of the other radiators. Once steam is allowed into the returns, all kinds of problems can occur (condensate being held up in the radiators, spitting radiator vents and water hammer)!
When you install a boiler feed unit, all the returns must drain into this receiver. The only way water can then enter the boiler is by activating the feed pump with a pump controller located on the boiler. Since this receiver can’t withstand any pressure, it is vented to the atmosphere. As a result, all of those former wet returns now have no backpressure from the boiler to offset the pressure from the supply side. Now the steam can reach down into those former wet returns and shove all that water back and forth in the piping, eventually showing up at the vent pipe, filling the boiler room with steam. Of course, in the process, the water hammer is incredibly loud.
The answer to this problem is to install F&T (float & thermostatic) traps at the base of each riser drip and at the end of each main, as well as radiator traps on each radiator. These traps will prevent the steam from entering into the return lines and pour out of the receiver’s vent line. Unfortunately, sometimes it isn’t economically feasible or even possible to install all those traps. The cost of removing the asbestos alone can be excessive, in addition to material and labor. When faced with these circumstances, many people will try to get away with installing one “master” F&T trap right at the inlet to the receiver. They figure this will prevent the steam from showing up at the vent pipe. It might, but it does nothing to prevent the steam from still reaching all the way down into those former wet returns, creating water hammer and other problems. Remember, the returns are now isolated from the boiler’s back pressure because they all drain into the vented receiver.
There is one other way of getting the job to work with the new boiler and boiler feed unit without having to use a box full of traps. It is called creating a “false water line.” By creating this false water line, you can keep the old wet returns pressurized and full of water just the way they were in the original system. This eliminates the need for all the steam traps.
There are several methods used to create this false water line. The following is one of those methods: install a 2″ F&T trap and hang it right near the boiler feed unit. You want the trap mounted so that its location closely mimics the water line of the old boiler. The style trap should have two inlet and two outlet tappings. Combine all the wet returns from the system into one common line. Pipe this line straight up from the floor into one of the trap’s inlet connections. Then, run a steam line from the steam main over to the other inlet connection of the F&T trap. This equalizing line puts pressure on the backside of the wet returns, keeping them wet and pressurized. This pressure acts to balance off the steam pressure from the supply side. Next, pipe a line from one of the trap’s outlet connections to the feed tank’s inlet connection. As the condensate forms in the system, the F&T trap will open to drain this returning condensate back into the receiver. It is important that the new water line be high enough to cover everything that was originally covered by the level of the old boiler’s water line. At the same time, if it is established too high, there is a chance the water could back into the main, causing water hammer and damage any of the system’s main vents.
The next time you are faced with replacing a boiler in an old building and the replacement boiler needs a boiler feed unit, check to see what type of piping arrangement the system uses. Creating a “false water line” may be the solution to that system!
If you have any questions or comments, e-mail me at [email protected]m, call me at (800) 423-7187 or follow me on Twitter at @Ask_Gcarey. ICM
I received a phone call from the owner of an oil company in the Boston area whose customer had a steam boiler that failed and needed to be replaced. His salesman went out to review the system and come up with a quote.
He came back to the office with a question. The system was a two-pipe steam system, but there were no traps on the outlet of any radiator. The salesperson had never seen a system like that and was looking for advice before he quoted the customer on a new boiler. The owner called me to find out what kind of trouble they could be getting themselves into if they proceeded. I talked with him about how two-pipe steam systems with dry returns have to operate.
A two-pipe steam system with dry returns has to have traps on the outlet side of every radiator. It has to! Why? First, we need a good understanding of what a dry return is. When they say dry, it doesn’t mean it is always dry. It will, in fact, get wet any time condensate is flowing from the radiator and back to the boiler room.
The dry part refers to if the piping is above or below the water line of the boiler when the steam system is off. If it is above, then it is filled with air whenever the system is off—that constitutes a dry return. Dry returns are also connected to each other above the boiler’s water line. As the individual radiator returns work their way back to the boiler room, they connect into a common return line that brings back all the radiation’s condensate back to the boiler room. Once in the room, a main vent is normally located near the end of the return before it drops down towards the floor, where it then becomes known as a wet return. Why? This section of piping is always below the boiler’s water line.
Back to the reason why two-pipe systems with dry returns have to have traps located on the outlet of each radiator—if they didn’t, the steam would travel past the radiator and get into the dry return piping. That’s where the problems begin! When a steam system is working properly, there is a difference in pressure between the supply and the return side of the system. If that difference “goes away,” the steam will stop dead in its tracks. Without pressure differential, there is no motive force, no reason to flow out into the system.
When the guys called me and told me they were working on a two-pipe steam system that has dry returns but no traps—I told them to go back and really check! When they got back, the answer was the same—there were no steam traps connected to the radiators, only union elbows or little P-trap elbows!
Congratulations, I told them, you are now working on a very old vapor or vapor/vacuum steam system. Back in the day, before thermostatic radiator traps were developed, heating engineers were forced to experiment with various methods to stop steam from passing through a radiator into the return portion of the system. They knew that if the steam passed into the return, the system would not work effectively. These union-elbows actually had a dip-tube like structure on the inside of the radiator that “dipped” down below the water seal that sits at the bottom of every radiator. These dip-tubes also had a very small hole located above the level of the water seal to allow air to vent out of the radiator. A small amount of steam would pass through the hole but would quickly condense as it left the radiator.
Most of the questions I receive are centered on the failure of the existing boiler plant, which now needs to be replaced. In addition to the normal concerns of replacing a steam boiler, because of the “weird” steam traps, contractors ask if there is anything else they should be concerned with. The answer can be tricky. One option is to leave everything as-is and “kind of hope for the best.” If the new boiler doesn’t need a feed tank to support the lack of water in the replacement boiler, and the dry returns are in good shape and pitched in the right direction, the home can probably survive the replacement.
I would suggest changing from the pressuretrol that comes with the new boiler to a vapor-stat. These systems by their very name—vapor or vapor/vacuum—indicate they were designed to run at very low pressures, ounces in fact. A vapor-stat, though more expensive, is much more accurate in controlling the pressure in the system to ounces. Because the vapor-stat will operate the system in ounces of pressure instead of pounds, it becomes critical to use the largest capacity main vents installed at the end of the dry return(s). The new boilers are physically smaller, holding less water. They are more apt to build pressure quickly, especially if the air in the system can’t get out quickly and effortlessly. By replacing the old vent with a large capacity vent, you can prevent the new boiler from short-cycling.
If the replacement boiler does require a feed tank, then the stakes are raised. I would strongly suggest replacing all of the old dip-tube style traps with thermostatic radiator traps. With a vented feed tank that’s open to the atmosphere, you have to ensure that the steam can’t get past the outlet of each radiator or it will eventually blow out the vent pipe, filling the boiler room with steam. This obviously makes the job more expensive, but if you try to use a feed tank with the old style dip-tube traps, you are creating more trouble for yourself! You will also have to install an F&T trap at the end of the steam main to keep the steam in the supply-side only of the system. The vapor-stat isn’t quite as important if new radiator traps and a feed tank are installed.
The important thing to remember is that when you come across a two-pipe steam system and it has dry returns, there has to be some type of “trapping” device on the outlet of each radiator, and it has been there from the very beginning.
If you have any comments or questions, please call me at 1-800-423-7187, Tweet me at @Ask_GCarey or E-mail me at [email protected]m. ICM
Why Polypropylene?
Polypropylene is environmentally-friendly, designed for sustained flue gases up to 230°F (110°C) and provides performance properties better suited to handle flue gases than polyvinyl chloride (PVC) or chlorinated PVC (CPVC) technology.
The polypropylene flue gas vent system is specifically engineered for the intended application. Polypropylene has a vicat softening temperature that exceeds 300°F (meaning the temperature at which the thermal plastic deforms under the load). The polypropylene vent pipe has higher temperature ratings and enhanced corrosion resistance to the acidic properties of the condensate associated with high-efficiency appliances.
Unlike other polymeric or metal systems, polypropylene is resistant to aromatic hydrocarbons, sulfuric acid and hydrochloric acid, which allows it to be used with oil-, propane- and natural gas-fired high-efficiency appliances. It is only limited by the flue gas temperature, making it an ideal choice for condensing heating appliances.
Editors note: Polypropylene venting is also an ideal choice for oilheat non-condensing dilution air boilers, which run with appropriately low vent temperatures and are approved for use with polypropylene venting. Several systems have gained market acceptance in the United States for over a decade, and are also now rated for use with B20 fuel blends.
Polypropylene vent systems are manufactured specifically to perform as a vent system. All the various and necessary components, such as test ports, siphons and condensate drains, are available to install the proper vent system. There is no need to modify the vent system to analyze the combustion numbers or drain excessive condensate from the vent system. The manufacturers offer single-wall pipe, flexible pipe, as well as concentric pipe, so regardless of the structure type, the flue gases from the condensing appliances can be safely vented out of the building to the atmosphere.
The polypropylene venting systems do not use glues and primers to join the lengths of pipes and fittings together. Instead they use a gasketed system to seal each connection point. The gasket technology allows the vent system to be installed rapidly; there is no need to rough-in the fittings as the components can be rotated in place, as well as disassembled. Once the venting system is completed, the high-efficiency appliance can be fired off immediately because, unlike glued systems, there is no 24-hour curing period required.
These polypropylene gas vent systems are designed to be used on condensing heating appliances that can produce one gallon of condensate per hour per hundred thousand British thermal units (BTUs). It is important that the vent system has proper pitch back towards the appliance, while the flue gases flow in the opposite direction towards the vent termination.
The pitch ensures that condensate is not allowed to build up in the vent system, which can cause back pressure leading to a forced shut down of the furnace or boiler. Also, build up of condensate gathering around a gasket can become a leak path, so good pitch allows the condensate to slide past each connection joint all the way back to the condensate trap.
A little history
Polypropylene gas vent systems have been around since 1994 for the European high-efficiency boiler market. The system is listed to the CE EN 14471 Safety Standard; the technology has proven to be safe and reliable. It is the dominating technology in Europe with millions of installations and is utilized by all the European heating equipment manufacturers.
This question comes up from time to time: Is PVC used for venting flue gases in Europe?
The answer is: No, Europe does not use PVC because of its lower maximum operating temperature and environmental health and safety concerns.
Manufacturers of these polypropylene gas vent systems arrived in the U.S. in 2009 and have sold and installed them for the last 13 years. One of the first things they did was obtain the UL-1738 listing to meet the most stringent and applicable safety standard used in the U.S.
Which leads us to the next question…Why UL 1738? The manufacturers of polypropylene gas vent systems had already been listed with Europe’s highest safety standard for venting flue gases from condensing appliances. They realized that, to participate in the U.S. market, they would need to be listed with the highest standard—Underwriters Laboratory-1738 (UL-1738). European manufacturers had an entire polypropylene vent system shipped to the lab to go through exhaustive testing procedures.
The reason why achieving a listing to the UL-1738 standard is so difficult is because there are several additional tests it puts the venting systems through that no other testing standards conduct:
Pressure Testing:
The vent system is tested to 250% of the rated operating pressure.
Leakage Testing:
The highest pressure is used to perform the leak test (3 L/H Max at 100Pa).
Low Temperature Handling:
A drop test is performed at -20°C (-4°F)—requiring no shattering, chips or cracks.
UV Testing:
This involves a 180-day UV Climate Chamber test.
High Temperature Testing:
The vent system is tested 70°F higher than the rated temperature.
Needless to say, the polypropylene gas venting system is a viable option to use when venting the flue gases from a high-efficiency condensing appliance. Because it uses a gasketed technology and not a glued technology, there are some installation details that are very different from what the industry may have been used to over the years. That is why the provision of installation instructions is the most important requirement of gas venting systems manufacturers wanting to be listed with UL-1738. Per the Standard, “Installation instructions shall be illustrated and include directions and information necessary to complete the intended installation of the venting system.” Can you imagine that? ICM
If you have any questions or comments, E-mail me at [email protected], call 800-423-7187 or follow @Ask_Gcarey on Twitter. ICM 
Over the last 10–15 years, installing high efficiency gas-fired condensing appliances has become quite common in residential and light-commercial applications. The industry has been moving towards higher efficiency products and utility companies have and will continue to offer rebate incentives to their customers to adopt this technology.
Question: What makes these appliances more efficient than the boilers and furnaces that are being replaced?
Answer: They intentionally condense the flue products that are created during the combustion process.
When a gas boiler or furnace is firing, the flame that is produced through the process called “combustion” passes through the heat exchanger. The other side of the heat exchanger is either air (if a furnace) or water (if a boiler), which absorbs this heat through conduction. The flue gases, which are the result of this combustion, are then vented out of the appliance through the vent piping (B-vent or a chimney), out of the building and into the atmosphere. The flue gases are hot enough that they remain in their gaseous state until they exit the building. It is this temperature of the flue gases that impacts the stated efficiency of the appliance.
As energy prices have become more of a factor all over the world, the heating industry has been looking for higher efficiency-rated appliances that will allow the consumer to get more bang for their buck. The manufacturers modified the design of their heat exchangers so that they could condense the hot flue gases that normally would pass through the vent system and out to the atmosphere. By condensing the gases (changing the flue products from a gas to a liquid), latent heat is released, which increases the efficiency of the appliances up to an additional 10%! When these flue products turn back to condensate (a liquid), the liquid is very acidic and corrosive, which is why most appliance manufacturers have chosen stainless steel as the material to use when designing and building their heat exchangers.
Venting materials
Not all of the flue gases will condense while in contact with the heat exchanger and will enter into the venting system. The industry quickly learned that the traditional vent materials (B-vent, masonry and clay chimneys) could not withstand the acidic nature of the condensate. Manufacturers then started looking for other materials to use that would withstand the corrosive condensate. Stainless steel vent pipe was an obvious choice, but also quite expensive. Plastic pipe was the other option that the industry selected as an alternative to handle the acidic condensate. The plastics included pipes made of polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) and polypropylene (thermoplastic polymer, PP). They are all classified as plastic pipe but each one has its own characteristics based upon its chemical makeup.
North American appliance manufacturers immediately adopted PVC, CPVC and stainless steel as their suggested vent pipe materials for their condensing products. PVC became the more popular vent pipe material of choice because it was the least expensive and readily available. In addition, every wholesaler in the plumbing and heating business had it in their inventory. Besides, plumbers were already accustomed to using it for most of their plumbing jobs.
Europe decided to go in a different direction. They chose polypropylene for their venting material to handle the flue gases for condensing boiler installations. One big difference to point out is that the polypropylene vent pipe was manufactured for one purpose—to vent the flue gases from these condensing appliances. The manufacturers engineered the vent pipe to be assembled as a complete venting system—from the appliance all the way to the termination. The manufacturers in Europe never considered using the other plastic piping (PVC or CPVC) to vent the condensing flue gases.
As European boiler manufacturers gained market share in the Northeast, and the condensing boiler market developed due to rising energy costs and rebate incentives offered by the utilities for higher efficiency appliances, polypropylene manufacturers decided to enter the North American market. Realizing that most contractors and wholesalers didn’t know who or what polypropylene piping was, the manufacturers needed to establish some credibility with their product. They approached Underwriter’s Laboratories (UL) and asked to test their highest venting standard in the U.S. UL1738 is considered to be the most stringent safety testing standard in the U.S.
In our next issue, we will discuss how this polypropylene venting system actually works, the benefits of using this type of venting system and answer some of the frequently asked questions about why gaskets (instead of glue) are used to seal each joint.
If you have any questions or comments, e-mail [email protected], call 800-423-7187 or follow me at @Ask_Gcarey on Twitter. ICM
The heating industry has been focusing on improving the combustion efficiency of the boiler, and every boiler manufacturer has a modulating/condensing boiler in its product offering. The number of mod/con boiler installations has been growing every year and will continue to grow. Some of the boilers, when installed in the right application, are achieving efficiencies in the 95%+ range.
Some in the industry are under the impression that, with thermal efficiencies this high, there isn’t any room left to improve a hydronic heating system. Their thinking would be correct if combustion efficiency was the only goal. However, there is another efficiency that the industry is starting to look at—hydraulic efficiency of the distribution system. We should be looking at overall system efficiency, which includes how efficient the boiler plant converts fuel into heated system water and how efficiently this heated water is delivered to the building.
Definitions
Let’s first define what Distribution Efficiency is:
EFFICIENCY = Desired OUTPUT quantity/ Necessary INPUT quantity
In basic terms…how much energy is needed to get the desired output?
When we apply the definition of distribution efficiency to a heating system, it looks like this:
DISTRIBUTION EFFICIENCY
= Rate of heat delivery/ Rate of energy use by distribution equipment.
If a heating system provides 120,000 British Thermal Units/hour (BTU/H) at outdoor design conditions, and they have four circulators that consume 90 watts each, the Distribution Efficiency for that system is:
DE = 120,000 BTU/H/ 360 watts = 333 BTU/H / watt
Compare that to a warm air furnace where the blower motor consumes 1,050 watts while delivering 110,000 BTU/H through the duct system. The Distribution Efficiency for that system would be:
DE = 110,000 BTU/H / 1,050 watts = 105 BTU/H/ watt
The hydronic system has a higher Distribution Efficiency than the warm air furnace because the physical properties of water are much better for conveying heat than air.
Even though hydronic systems generally have a higher Distribution Efficiency than air systems, when the number of pumped zones increases, the Distribution Efficiency can quickly dissolve. For example, I recently visited a very large home that had 34 zones, all with water-lubricated circulators consuming 90 watts each. The house had a design load of 350,000 BTU/H. When you run the numbers to determine the Distribution Efficiency:
DE = 350,000 BTU/H / 34 x (90 watts) = 114 BTU/H / watt
As you can see, a hydronic system, when taken to the extreme, can become an inefficient distribution system. These systems have been installed for years with no real concern for operating costs. However, with energy costs continuing to rise, not only has it has impacted both fuel costs for transportation and heating homes, but electrical costs are also impacted.
Electrical power plants need to use some source of energy. The majority of plants have used coal for years, but through legislation, many are being closed down or converted to natural gas. This is putting tremendous pressure on the power plants to manufacture electricity. The result? Higher electric bills!
Over in Europe, where they have experienced higher fuel and electric costs, they have been forced to come up with better and more efficient ways to heat water and deliver the heated water to the heating terminal units. One of the technologies they have embraced for years is electronically commutated magnetic
motors (ECM).
The majority of residential homes in Europe use hot water heating to warm their homes. To achieve higher Distribution Efficiencies, they have incorporated ECM technology into their circulators. In fact, nowadays, only ECM circulators are allowed to be installed in Europe.
The pump manufacturers in Europe have combined their efforts to improve the efficiency of the circulators they offer for hot water heating systems. They came up with an efficiency index that all pump manufacturers had to reach called the Energy Efficiency Index (EEI). The European community created legislation to adopt this EEI standard and manufacturers quickly realized they could not achieve the necessary efficiency points with induction motor technology. It just proved to be too inefficient, so they moved to ECM technology.
Back in the Northeast
Utilities in the Northeast are providing rebate incentives for residential ECM circulators. It seems they are very interested in having the hydronic industry move away from the old, inefficient induction motors and move towards ECM technology. Plumbing and heating wholesale distributors have signed up and became part of the utility’s high-performance circulator program. This allows them to offer a $100 discount off the price of any of the participating ECM residential circulators.
Why would they provide such a generous incentive? It has to do with energy costs and energy consumption. As energy costs continue to rise, the impact affects everyone. As production costs go up, distribution costs go up, and the net result is higher utility bills for end-users.
If we were to re-examine our Distribution Efficiency formula while incorporating the new ECM circulators that can consume considerably fewer watts, the Distribution Efficiency can be markedly improved. If we go back to that large home that had 34 water-lubricated zone pumps and replaced them with the ECM pumps with speed control (which allows the pump to be set for the zone’s actual load) the formula would look something like this:
DE = 350,000 BTU/H / 34 x (20 watts) = 515 BTU/H / watt
If you have any questions or comments, e-mail [email protected]; call 1-800-423-7187 or follow @Ask_Gcarey on Twitter. ICM
Circulators have been around the hydronic heating industry dating back to the late 1920s to the early 1930s. They were originally added to existing gravity hot water jobs to “boost” the heat around the system. In fact, Bell & Gossett marketed its circulators as “Booster” pumps because they would move the heat from the boiler to the radiators much faster than simply by gravity.
These original circulators were often referred to as “three-piece” pumps because they had three distinct sections—the wet end or volute where the impeller is located; the motor end (which is the driving force) that would mount in a cradle; and a bearing assembly that would connect the two ends together with a coupling assembly. The motor assembly was completely separated from the wet end of the pump by a seal. The bearing assembly would be lubricated with oil to keep the bearings in good working condition. These pumps dominated the hydronics industry for decades and did a very good job.
Sometime in the 1970s or early 1980s a new style of pump came onto the scene that changed forever the residential (and eventually light commercial) market. These “new” circulators used the system’s own water as its lubricant. There was no longer a need for a separate bearing assembly and seal. The physical size of these pumps was considerably smaller and they cost much less than the three-piece style. At first, there were many skeptics about the new pump’s ability to perform as well as the original, larger pumps. However, over time, the industry realized these new “water-lubricated” pumps worked quite well, lasted a long time, required virtually no maintenance and were less expensive.
Over the past 10 years, some pump manufacturers have been offering multi-speed pumps that offer a different pump curve for each speed. The most common is a three-speed wet-rotor circulator that offers three different performance curves. The benefit is that, with one pump, you can provide three different curves to meet various system conditions. From an inventory standpoint, you can stock (on the shelves or in the service truck) one circulator model that can meet many different system applications.
Imagine 10 speeds or even 50 speeds instead of just three speeds—and for each speed change, you could plot a new pump performance curve. The highest speed would represent the pump’s maximum performance and the lowest speed would represent the pump’s minimum performance. A variable speed pump can operate anywhere between these two points simply by varying the speed of the motor.
Any wet rotor pump with a permanent split capacitor motor can function over an extensive range of speeds with a variable speed controller. This device varies the frequency of the alternating current (AC) signal sent to the permanent split capacitor (PSC) motor. By varying the AC signal, the rotations per minute (RPM) of the motor (the speed) are changed, which directly changes the flow and head capacity of the pump. The changes, and therefore the pump curves, are unlimited between the fastest and slowest RPMs of the motor. One popular application uses a standard wet rotor pump controlled by one these variable speed controllers to provide injection mixing for any low-temperature heating system.
The new circulator—ECM
A new style of “smart” pumps has made its way into the North American hydronics market. They are called ECM pumps, which stands for electronically commutated magnetic motor. They are very different from the PSC motors we have been using in our wet rotor pumps. This new style motor is sometimes called a “brushless DC” motor. The rotor in this ECM motor has permanent magnets instead of wire windings that are separated from the system fluid. The magnets are located inside a stainless-steel rotor can and react to the magnetic forces created by electromagnetic poles in the stator.
Here is where you may experience a problem with the new ECM circulators. These onboard magnets can do a very good job of collecting/attracting iron oxide from the water in the system. Iron oxide is a chemical compound consisting of a mixture of oxygen and iron. Every hydronic system has some oxygen (from the system water [H2O]), and more often than not, some type of iron, ie.; cast iron from circulator volutes, flow-control valves, cast iron boilers, cast iron radiators and black iron steel pipe.
Every system can contain a different amount of iron oxide, which will influence whether the ECM circulator “attracts” enough of it to cause the pump to stop running. I have heard of several instances where the contractor isolated the pump, pulled the can from the wet end of the pump, cleaned off the buildup of iron oxide, put the pump back together and it ran fine afterwards. Other times they ended up having to replace the pump because too much damage had been done.
There is a simple solution to this and it’s not to go back to the old-style wet rotor pump—that horse has already left the barn. The utilities have been playing a big part in creating incentive programs to promote the installation of these “High Efficiency” pumps, similar to how they played a big part in the industry’s adoption of modulating/condensing (Mod/Con) boilers. Europe has been installing high efficiency boilers for years (having outlawed the PSC wet rotor pumps because they consume too much electricity) and installs high performance dirt and magnetite separators as standard design practice.
If you are installing high efficiency boilers and ECM pumps (by law), then you want to ensure the quality of the water circulating through the system. As the industry continues to install these high efficiency ECM pumps, it should become standard practice to also include a magnetic dirt and iron oxide collector to protect the new high efficiency equipment.
The efficiency of these “Greener” circulators was designed to meet the ever-increasing efficiency standards that have made their way over to North America. Their “wire to water” efficiency is simply higher than the PSC wet rotor circulators. Their multiple application capabilities with the onboard microprocessors and their reduction in wattage consumption make them a very compelling alternative to what we have used in the past. ICM
If you have any questions or comments, e-mail [email protected], call 800-423-7187 or follow @Ask_Gcarey on Twitter.
There have been many condensing boilers installed during the past few years that operate with natural or propane gas as their fuel source. They are called “high-efficiency” boilers because they have efficiency ratings in the 90s…some as high as 95%. To attain such high efficiency numbers, they intentionally condense some of the flue products that are formed as the result of combustion.
Normally, we would make sure that the boiler never condenses its flue products because, if allowed to, the condensate could damage the boiler and vent piping. When combustion occurs, energy in the form of heat is transferred through a heat exchanger (pinned cast-iron sections, copper-finned tubes, cast-aluminum and stainless-steel heat exchangers) to flowing water, which is on the other side of the flame. When the flame is produced, combustion gases are formed. These gases contain water in the form of vapor.
Generally speaking, we want these vapor gases to vent out of the boiler, up into the venting/chimney system and out into the atmosphere. Condensing boilers are designed to allow the flue gases to condense right inside the heat exchanger. They even provide a condensate drain to allow the condensate to escape from the heat exchanger and drip through a neutralization kit into a drain or condensate pump.
The benefit of condensing these combustion gases is that they contain heat or energy that we normally lose up the chimney. Just like in a steam system, when the water in the form of vapor (combustion gases) condenses, it gives off a lot of latent heat. How much? For every pound of water vapor that condenses back to liquid, 1,000 BTUs of latent heat are released. The heat exchanger “catches” this heat and transfers it over to the system water. This is how these condensing boilers achieve higher efficiency ratings. More of the unit of fuel goes into heating the system water rather than up the flue pipe.
Inner workings
Just how are these flue gases condensed? It is the exact opposite method of how we prevent these same gases from condensing in a non-condensing boiler. Condensing occurs naturally—when the combustion vapors cool below dewpoint, they will condense back to liquid. Water temperature has the greatest impact on whether the flue gases in a boiler will condense or not. It’s all related to the dewpoint of the combustion gases. Oil-fired systems want to keep the water above 140°F to prevent the gases from condensing, while gas systems generally want to be above 130°F to prevent condensing.
In a condensing boiler, the water temperature in the return needs to be 130°F or less for the flue gases to condense. With return water in that temperature range, the flue gases will condense and the boiler will operate at or near the published efficiency rating. Whenever the return water climbs above 130°F, which is higher than the dewpoint of the combustion vapors, those gases will not condense in the heat exchanger.
The particulars
The question often is, Can I use a high-efficiency modulating and condensing boiler in a system that incorporates traditional high temperature baseboard? Some people in the industry would say, No you can’t! The water needs to be hot enough to satisfy the baseboard’s requirements, which are too hot to allow any condensing of the flue gases! If you aren’t condensing the flue gases, why use a condensing boiler?
A large portion of these condensing boilers are sold in retrofit applications for both residential and commercial buildings. The boilers usually are cast iron oil-fired or atmospheric vented gas boilers and they serve high temperature terminal units such as copper baseboard or cast iron radiators.
When these systems were first installed, the radiation was sized so that on a design cold day, with water circulating through the radiation at 180°F, the room temperature could be maintained at 70°F. Due to these design conditions, the above comments can be made about compatibility issues between condensing boilers and baseboard radiation.
However, how often during the heating season do we actually encounter design conditions? Up here in the Northeast, design conditions make up about 3–5% of heating. The conditions are somewhere less than design during the rest of the year. In fact, through Bin Data collected by the National Weather Bureau, 80% of the heating season requires 50% or less of the BTUs needed for design conditions. In effect, the heating system, including the boiler and the installed radiation, is oversized for most of the heating season.
Proper application of Outdoor Reset
Outdoor Reset calculates the right water temperature for the radiation based upon the load that the house or building is experiencing. What has the greatest impact on a building’s load? The outdoor temperature! By simply incorporating the outdoor reset function that comes with the condensing boiler’s operating control, the boiler can start delivering the appropriate water temperature needed at the given set of outdoor conditions.
As you look into design conditions, reset curves and Bin Data, you see that for a large majority of the heating season, the boiler can lower the water temperature so the return temperatures coming back to the boiler are below combustion gas dewpoint levels. The boiler flue gases are now condensing; the boiler is operating at or near its rated efficiencies and the apartment building or house is comfortable.
When designing around 180°F water, 70°F indoors and a design outdoor temperature of between 0°F and 10°F, you will find that, until it gets down to 25°F or colder, the reset curve will calculate a water temperature that provides return temperatures below the dewpoint of the flue gases, ensuring the boiler is operating in a condensing mode.
Another benefit to this style of boiler is that, in addition to the condensing feature, the burner can modulate. This means that as the load changes, the boiler will consume only the necessary fuel to meet that load. Unlike traditional “On/Off” boilers—where, if they are firing, they are consuming 100% capacity—the modulating boiler can fire down to as low as 10% of its capacity and then modulate all the way up to 100%.
In a perfect situation, when using a condensing boiler, the radiation chosen should be able to provide all the BTUs needed with low temperature water. For that to occur, all of the existing homes and commercial buildings would have to change and/or upgrade their existing radiation. In some rare instances, that actually does happen—but the majority of the time it doesn’t.
Will the boiler condense all the time? No, but it will for the majority of the heating season. It will also modulate its firing rate to match the load that the building is experiencing. All of these features add up to reduced fuel consumption and more comfortable heating systems. If you have any questions or comments, e-mail me at [email protected] or call me at 1-800-423-7187. ICM
In the past, underground snow melting of a driveway or walkway for residences had been considered a luxury and perceived as too expensive to install and operate. However, over the years, I’ve seen the number of snowmelt systems installed in residential homes increase quite a bit. The scenario may have been renovation of an existing home that included replacing or upgrading the driveway or it may have been part of a newly constructed home’s design.
Regardless of the situation, it has become increasingly common to install a snow melt system but, unlike other traditional heating systems, once the tubing is installed and piped, it is fairly difficult to fix a design flaw. This is why I find the quote from Bell & Gossett as relevant today as it was 56 years ago: Snow melting systems have been used for many years in commercial installations such as store front walks, parking garage ramps, loading docks, etc. In these installations the protection against slippery pavement is complemented by the elimination of tiresome and messy jobs of snow shoveling or plowing.
The benefits of snow melting systems can carry over into the residential field quite easily. The necessary equipment for a well engineered snow melting system is easily adaptable to any standard hot water boiler. Two of the major limitations to wider acceptance and use of snow melting systems are cost and lack of proper design information. These two characteristics go hand in hand. (1966 Bell & Gossett Snow Melting System Design Manual).
Snowmelting does have some design issues, as well as operating issues, that both you and your customer need to discuss. First, once the customer gets past the installation cost, the next question is always: How much does it cost to operate? The answer depends on a lot of issues, such as how much snow needs to be melted, how quickly it needs to be melted, if the customer “idles” the driveway at some minimum temperature and how cold it is outside. Based upon some standard conditions here in the Northeast, the following example can be used to approximate what it may cost to operate your snowmelt system during a snowstorm. If you have a 1,000 square foot driveway and the snowmelt system provides 200 British Thermal Units (BTUs)/hour per square foot surface area, you would need a boiler capable of providing at least 200,000 BTU/h. In our example, the snowmelt system ran for 10 hours to melt the driveway, so you would consume 20 therms of natural gas or about 16 gallons of oil. Based on the cost of either a therm of natural gas or a gallon of No. 2 fuel oil, you could calculate the cost to melt the snow during that single event.
Controlling the melt
How the snowmelt is controlled plays an important part in the cost to operate the system. There are many ways of operating a snowmelt system. They can be turned “on” and “off” manually, automatically and somewhere in between. From an economic standpoint, the system should start as soon as it detects snowfall and turn off as soon as the snow is melted off the driveway. This is probably the least expensive way to operate and still maintain all the benefits of a snowmelting system.
You will want to have a conversation with your customers regarding the expectations they have on what they think their snowmelt system can (and can’t) do. Some people think that when it starts snowing, they can invite their friends over for a snowmelt party. You will want to make sure they understand there is a “time-lag”— it takes time for the snowmelt system to heat up the slab and bring it up to a melting temperature. Once it reaches the melting temperature, the system will continue to run until the automatic snow/ice sensor senses that it is dry and shuts the system off until the next snow fall. This operation may last 4–5 hours and quite possibly longer depending upon the amount of snowfall, how long the storm lasts and the outdoor temperature. You will want your customer to understand this up front, before the first snowfall.
In some applications (usually commercial and industrial), customers can’t wait that long for the snow melt system to activate. Instead, they operate the system in what’s known as an “idling” condition. Most snowmelt controls have a feature where you can set the snow/ice sensor to maintain the slab at some minimum temperature, typically 33–35°F. This gives the snowmelt system a “running start” so that when the snow starts falling, the slab does not have to be heated from a cold starting point.
This, of course, costs money. You are heating a slab all the time, so regardless of outdoor temperatures and wind speeds, you are “pumping” BTUs into the ground. This is another thing your customers need to know when discussing their expectations of the system.
Designing the system
In a residential application, a snowmelt system is a convenience item. You don’t have to wait for the plow guy to show up; you don’t have to shovel the driveway; you don’t have to salt your driveway and walkway and the system can start and stop automatically. However, it does take some time to get up and going before the melting starts.
From a design standpoint, you can use any of the radiant tubing manufacturers or their representatives to help you design and lay out the system. They will be able to help you calculate the actual load, select the right size and amount of tubing, how to best lay out the tubing, the correct design water temperatures, as well as offer a control and piping strategy to operate the system.
In general, there are a few design issues that should concern you. The first issue is if you are going to use the existing boiler to melt the snow. Does it have the capacity to handle this extra load? If not (probably the case in most systems), are you going to dedicate a boiler to just snow melt? This does happen often, but I think a better design is to add the additional boiler to the existing boiler, piped as a multiple boiler plant. Then by adding a plate and frame heat exchanger, which is dedicated to the snow melt system, you can have backup capabilities, rotation and all the other features that come with a multiple boiler system.
When the snowmelt system first turns on, it is very important that the slab/driveway does not get “shocked” with hot water. The control system has to monitor the heat input to the slab in a controlled manner to protect the slab. If not, the driveway will possibly experience cracking. The same issues exist in the boiler room. It is important to prevent large slugs of extremely cold water from entering the boiler(s). This could cause thermal stressing and eventual cracking of boiler sections.
If standard, non-condensing boilers are used, the control system has to prevent flue-gas condensation from occurring for extended periods of time. If not, the system will damage the flue piping and eventually the cast-iron sections. All of these issues can be handled easily with proper piping and a proper control strategy. Again, something that the radiant tubing manufacturers deal with in every system they design.
If you have any questions or comments, contact me at [email protected] or 1-800-423-7187. ICM
Mother Nature has a collection of “rules” that govern how things work in this world—“High pressure goes to low pressure,” “Whatever goes up must come down,” “For every action there is an equal and opposite reaction” and probably her most famous if you are in the heating industry, “Heat goes to cold!” If you were to ask someone where does heat go? he/she would say heat rises. That’s not necessarily correct, since hot air rises, but heat goes to cold, always. Mother Nature hates an imbalance and, when it exists, she does everything in her power to equalize or balance it.
When your heating system delivers warmth to your house, it eventually leaves through the windows, roof and siding. Why does the heat leave? There is an imbalance between the temperature inside the house and the temperature outside. Heat goes to cold…always! The same thing happens in the Summertime. When it is very hot outside and your house is cooler inside, the heat outside wants to go to the cooler indoor temperature.
How do we typically make the indoor cooler? Most people would say the air conditioner, which is true, but how eludes most people. We use an air conditioning system that removes heat from the indoors and sends it outside. That’s because you can’t make cold. To create a cooler atmosphere, you have to remove the heat, which is the basis of refrigeration. Whenever you feel cold, it is caused by a lack of heat.
If we know that heat wants to go to cold, why do we call it a heat pump? Why do we have to pump the heat when heat normally goes to cold? The reason is a heat pump, rather than creating heat, simply moves it. For example, it can move thermal energy from the cooler outdoor air into the warmer inside room. It pushes heat in a direction counter to its normal flow (cold to hot rather than hot to cold), hence the word pump. A boiler or furnace burns fossil fuel to create heat. A heat pump simply uses an existing source of renewable energy, like the heat that exists in outdoor air. This can lead to a significantly reduced consumption of energy while providing comfort.
Refrigeration
The definition of Refrigeration is the process in which work is done to move heat from one location to another. It may also be defined as lowering the temperature of an enclosed space by removing heat from that space and transferring it elsewhere.
Refrigeration uses refrigerant to move heat as it changes state. Nowadays, the refrigerant of choice is R410A. Its properties allow the refrigerant to be a liquid well below freezing. It has a freezing point at -155°C which is equivalent to -247°F. It has a boiling point of -48.5°C which is equivalent to -55°F. As a liquid refrigerant, it absorbs heat when it evaporates into a vapor. When the refrigerant is in its vapor state, it contains all that energy; when it condenses back into a liquid, it rejects or expels the heat it originally absorbed.
You have to remember that phase change contains a significant amount of energy. For example, when you change the temperature of one pound of water from 211°F to 212°F, it requires one British Thermal Unit (BTU). When you change one pound of 212°F water to 212°F vapor (steam), it takes 970 BTUs that you “get back” when the vapor condenses back to its liquid state.
A heat pump incorporates the vapor-compression refrigeration cycle to move heat either away from an area where it’s not wanted (cooling) or moves heat into a space that needs it (heating). Because of the unique operating properties of R410A, an Air-to-Water or Air-to-Air heat pump has the ability to take heat (energy) out of the air that we would consider very cold but to the refrigerant considers it warm. This applies to the heating mode of the heat pump.
The cooling operation is identical to that of an air conditioner. Again, using refrigerant and the vapor-compression cycle, the cold liquid refrigerant flows through the air conditioning coil as room air blows across it. The heat from the air goes to the cold liquid refrigerant, thus leaving the air cooler than it was when it entered the coil. The absorbed heat “flashed” the cold liquid refrigerant into cool vapor, which will then flow outside to the compressor. There, the cool vapor will be compressed (by the compressor) into a high temperature vapor. The vapor, which is storing a lot of energy (the heat we wanted to remove from the home), is pumped through a condensing coil where a fan is blowing outside air across it. This outdoor air is hot, relative to our comfort, but much cooler than the temperature of the hot vapor refrigerant. The hot vapor transfers its energy/heat to the outside air, thus completing the process of removing heat from the house and condensing it back into a warm liquid.
Reversing valve
Heat pumps have the unique ability to either heat or cool a home through a simple device called a reversing valve. There are four key components required:
• evaporator
• condensor
• compressor
• expansion valve
By adding the reversing valve, the heat pump can “reverse” the role of these key components and provide heating or cooling from the same compressor.
Another term unique to heat pumps is Coefficient of Performance (COP). This term expresses how efficient the heat pump is with regards to the amount of energy it uses relative to the amount of energy it delivers. The term was developed to compare heat pump systems according to their energy efficiency. A higher value implies a higher efficiency between the pump’s consumption of energy and its output. Design conditions will impact the heat pump’s COP performance factor. Air-to-Air and Air-to-Water heat pumps have in the past been negatively impacted in their performance by colder outdoor temperatures. However, with advances in compressor technology, specifically invertor-driven compressors, these Air-to-Air and Air-to-Water heat pumps are capable of extracting energy (heat) from very cold outdoor temperatures and transferring the energy to the heating medium (water or air).
Contact me with any questions or comments at [email protected]; 800-423-7187 or follow me on Twitter at @Ask_Gcarey. ICM
