Recently, a contractor asked me what the correct way to size a replacement steam boiler was; he said he had heard conflicting ideas from different people within the industry. The proper way to size a replacement steam boiler is to go around and add up all of the radiation in the house. Back in the day, the expression used to indicate a radiator’s heating capacity was referred to as a “square foot of steam,” that came from the original flat steel radiators used back in the mid 1800s. They would measure how many actual square feet of surface area the panel radiator had to determine its heating capacity. One square foot of surface area from the radiator would put out 240 British Thermal Units (BTUs) when the air temperature around the radiator was 70°F and the steam temperature inside the radiator was 215°F. If a radiator had 20 square feet of surface area, it could emit 4,800 BTUs an hour. Also important to note, 1psig steam has a temperature rating of 216°F, so every radiator that has been installed in a steam system can offset the heat loss of that room with less than 1psig steam pressure at the radiator. If you try to solve a heating problem by raising the steam pressure, you’ll overheat the rooms and consume more fuel in the process. Almost from the beginning of installing residential steam heating systems, homeowners complained about the size and look of those flat, steel-plated radiators and so the industry responded. Radiator manufacturers started making tubular style radiators that took up less space and aesthetically were more pleasing to the homeowners. They were able to provide increased output in a smaller footprint by adding surface area to the tubes. This created a new term in the radiator industry: EDR which stands for Equivalent Direct Radiation. Because these radiators were not shaped like a panel radiator, it was challenging at the beginning to establish a square foot rating but eventually they figured it out and the term a Square Foot of EDR was born.
Back to sizing the replacement boiler — there are sizing capacity charts provided by various boiler manufacturers in the industry that will list a radiator’s heating capacity in Square Foot of EDR based upon the height of the radiator, the number of columns per section and the number of sections. Dan Holohan offers an excellent book that contains virtually every piece of radiation ever manufactured titled EDR…Every Darn Radiator. If you are in the business of replacing steam boilers, you should have this book. When you are asked to size a replacement steam boiler, the last thing you should be concerned with is the heat loss of the house. I know it sounds crazy, but it’s true. If you were replacing a hot water boiler, you would calculate the current heat loss and then select the correct boiler. In a hot water system, you are using a liquid to transport the heat from the boiler out to the radiation and this liquid is going to stay a liquid…cooler on its way back but still a liquid. However, with steam it is different. Steam is a gas that carries the heat from the boiler out to the radiators where it is needed. If you don’t produce enough gas (steam), the heat won’t reach all the radiators and you end up with cold rooms and unhappy customers. You have to produce enough steam to fill the piping and all the radiators. This is because steam wants to turn back into water as quickly as it can. When steam enters cold pipes and radiators, the cold metal robs the steam of its latent heat. With no more latent heat the steam turns back to a liquid (condensate). The idea is to have a boiler produce enough steam to overcome the system’s ability to condense it.
Steam is made up of two types of BTUs. The first type is called sensible heat. This is the amount of heat required to bring water to its boiling point. It can be “sensed” by a thermometer. At every pressure, there is a corresponding requirement of sensible heat to boil water (the higher the pressure, the greater the amount required of sensible heat).The second type of heat is known as latent heat (the heat of evaporation). This is the amount of energy required to take the boiling water and change it into steam. A thermometer can’t sense this energy, although it is very real. In fact, in a low pressure system (0-15psig), the amount of latent heat is usually five times as much as the sensible heat per pound of steam. Steam can hold a tremendous amount of energy while requiring no assistance to travel throughout the system.
When steam is manufactured in the boiler, it races out of the boiler into the piping system and towards the radiators. As it does, it encounters the cold pipes that cause the steam to condense back into water. During this condensing process, the steam gives back the latent heat it received in the boiler. In a steam heating system, this is what heats the rooms. It is not high pressure that heats the house, so there is no sense in turning up the pressuretrol. In fact, the lower the pressure, the greater the quantity of latent heat per pound of steam.
The problem arises when the boiler can’t produce enough steam to offset the system’s ability to condense it. The steam condenses in the near-boiler piping, supply mains and maybe in some of the closer radiators. The thermostat never lets the burner shut off. No matter how high you turn the pressure up, you can’t produce enough steam. One symptom I have consistently noticed is that the pressure gauge never registers any pressure when the boiler is undersized or underfired. The boiler can’t build any pressure because as soon as any steam is produced, the system condenses it.
When you install a replacement steam boiler, it is important that it be sized to the connected load. Once you have picked the correct size and have installed it according to the manufacturer’s specifications, make sure you also fire the burner to the connected load. If you don’t, the results can be the same as an undersized boiler.
You have to realize that just because the boiler manufacturer says it’s a steam boiler and supplies all the necessary trim, it doesn’t make steam by magic. You have to input enough energy so that the boiler can offset the connected load’s condensing ability. That means when the boiler is rated to a certain gallons per hour (GPH), you have to use that firing rate. If you don’t the boiler won’t be able to produce enough steam. The steam won’t be able to reach the furthest radiators because it’s condensing in the pipes.
If you have any questions or comments, e-mail me at gcarey@fiainc.com, call me at (800) 423-7187 or follow me on Twitter at @Ask_Gcarey.
Primary/Secondary pumping…It seems to have become the “catch-phrase” of the hydronics industry over the last few years and rightly so. Its applications are virtually endless and the benefits of this piping technique have solved many problems over the years. But where did this piping technique come from and WHY is it so useful?
An engineer from Bell & Gossett named Gil Carlson originally developed this piping technique. This is the same Gil Carlson who promoted the concept of “pumping away” from the point of no pressure change (placing the system circulators on the supply); he developed circuit setters to balance multiple circuits and developed a famous engineering tool known as the B&G “System Syzer”. He was instrumental in developing and promoting engineering principals and piping techniques as the world of hydronic heating developed.
As the story goes, Gil was called out to the field to troubleshoot a recently installed commercial hydronic system that was not working. It was a large garden-style apartment complex. The system was designed to operate as a “mono-flo” heating system. And as you know, a “mono-flo” system relies on one primary circulator to pump hot water around the heating main. Piped off this main are risers that feed the various pieces of radiation. Now remember this is not a two-pipe system where there is a separate supply and return main. With a “mono-flo” system, there is only ONE main and each riser’s supply and return pipe is connected to this single main. When the water is circulated around this main, what is going to cause some of the water to “jump off” and flow into the radiation circuit? That is where the mono-flo fittings come into play. From the outside, a mono-flo fitting looks like an ordinary tee, but on the inside there is a cone-shaped fitting that reduces the opening of the tee. This reduction causes pressure drop as the water flows along the primary main. And it is this pressure drop that causes a portion of the water to move off the main and into the radiation circuit. On the problem job that Gil was called out to troubleshoot, the water was flowing nice and hot along the main, but was NOT flowing up into the radiation circuits. After some investigating, he found out that two different engineering firms were involved in the system design. One was responsible for the boiler room and primary main piping. The other firm was responsible for the distribution piping throughout the buildings.
What happened was the primary main piping was significantly undersized and the distribution and radiation piping was oversized. When you put these two mistakes together in a large mono-flo system, the result is NO-HEAT throughout the complex! After much arguing and “finger-pointing”, Gil decided to try an idea. His thought was to install a small, in-line booster pump on the supply riser of each building. His idea was to turn on the booster pumps every time the main circulator was running. The booster pumps would be able to overcome the pressure drop of their own risers and radiation circuits, thus establishing the needed flow to heat the buildings. One problem that he had to contend with was the problem of installing all these smaller booster pumps in series with the larger primary pump. To overcome this problem, he came up with the idea of installing a piece of piping that was connected from the supply to return riser. The pipe, which he referred to as the “common pipe”, was common to both the riser circuit piping and the primary main piping. When all was said and done, the problems went away, the buildings heated as designed and a new and innovative method of pumping multiple circulators was born. By the way, this all took place back in the early 1950s!
The Simplicity of Primary/Secondary
Primary/Secondary Piping–Click to Enlarge
During this past spring season, we have presented several seminars. Of course, a lot of questions are asked during these classes. The following is a sample of some of those questions, in no specific order.
Q: Why should I offer my customers who have hot water boilers a weather responsive control?
A: Customers who have hot water heating systems have an opportunity to reduce their fuel consumption by adding an outdoor reset control to their boiler system. When a heating system is designed and installed, it has to be sized for the specific design conditions that occur in that particular area of the country. Up here in the Northeast, outdoor design temperatures can be anywhere from 10°F to as low as -20°F, but regardless of what temperature you use to size everything, these conditions occur for only 2-3% of the total heating season. For the rest of the season, the boiler and radiation is, in effect, oversized for the building. Systems that operate only on the boiler’s aquastat are subject to short cycling and noticeable temperature swings in the living environment. By installing an outdoor reset control, the water temperature leaving the boiler will change as the load on the building changes. The warmer it is outside, the lower the water temperature that will be needed for the radiation to operate. This will reduce any noticeable temperature swings and reduce boiler short cycling. The end result is a heating system that is more comfortable while consuming less fuel.
Why do the tees in a primary/secondary
system need to be located so close together?
When describing primary/secondary systems, this question comes up often. Why so close and what happens if you don’t install them close together. The tees need to be close together so that the operation of the primary circulator will not cause flow in the secondary circuit, and vice versa. You are trying to hydraulically isolate one circuit from the other. If the space between the tees becomes excessive, the pressure drop between the tees increases. This will cause some flow/heat to move into the secondary circuit from the primary loop, regardless of whether the secondary circuit wanted the heat or not. In effect, you have lost control of the system. You will experience overheated zones and comfort complaints.
When I am replacing an old steam boiler with a new one, why do I need to count all the radiation in the house?
Why can’t I do a heat loss on the house and size my boiler based on this information? The reason the radiation load needs to be calculated—unlike a hot water installation, where water fills the entire system—is that in a steam system, air occupies all the piping and radiation above the boiler water line. Also, water is the heating medium in a hot water system. The boiler heats the water, which then travels throughout the system, Although it takes a temperature drop, it never changes state; it leaves as water and comes back as water (just a little cooler). In a steam system, we have water that is heated in the boiler to a point where it changes into its gaseous state (steam). Then the steam leaves the boiler and enters the piping system where it encounters cooler surfaces (steel pipes and cast-iron radiators). The cooler temperatures cause the steam to condense back to water.
When this happens, the energy that was required to change the water into steam is released. If your new boiler can’t produce enough steam to fill ALL the radiators, then some rooms are going to remain cold. Using the heat loss method doesn’t help, because the steam doesn’t know anything about heat losses. All it knows is cold metal, so your job is to make sure the new boiler can overcome the “condensing action” of all the pipes and radiators.
Why can’t I pipe the new steam boiler the same way as the old boiler that I’m taking out?
Older steam boilers had three important characteristics that helped them produce good dry steam. First of all, the section-width was wide, allowing the steam bubbles to rise to the water surface calmly. Once at the surface of the water, the steam chest was cavernous, allowing the water and steam to separate efficiently. Lastly, the exit hole diameter was designed to limit the steam’s exit velocity to 15 FPS. This ensured that only dry steam left the boiler and entered the system piping. Because of these factors, the installers could attach the boiler to the system piping with some “interesting” methods. The problem with attempting that today is the fact that a modern steam boiler is lacking in all those areas. The section width has become narrower, causing a “frothy-like” mixture of steam and water to occur as the steam bubbles try to pass through the water. Also, the steam chamber is virtually non-existent in the new boilers. Finally, size of these exit holes is smaller and there are fewer of them. This INCREASES the steam’s velocity as it leaves the boiler, which increases the chances of pulling water up out of the boiler with the steam. With modern steam boilers, it becomes very important to pipe the new boiler according to the manufacturer’s installation instructions. The near-boiler piping has taken on the responsibility of producing dry steam. If you ignore the instructions, there is a good chance you will have problems.
When troubleshooting two-pipe steam systems, why is it OK to use temperature as an indicator when searching for bad radiator traps, but not for the end of main F&T traps?
Radiator traps are also called thermostatic traps, and as the name implies, temperature affects the operation of the trap. When steam arrives at the radiator, it elevates the temperature around the trap causing it to close. When the steam condenses and turns back to condensate, the temperature cools down, allowing the trap to re-open. So it stands to reason that temperature can be an indicator of a good or bad radiator trap. However, F&T traps (float and thermostatic) operate a bit differently. There IS a thermostatic element in there, but it only vents air through the trap. Any condensate that forms is drained off through a float and seat mechanism. However, the float doesn’t care about temperature, only displacement, which is caused by a volume of condensate. This means, technically, you could measure the steam’s temperature on the inlet side of the trap and measure almost the same temperature of condensate coming out of the trap. Therefore, temperature as an indicator can be very misleading! When troubleshooting F&T traps, a better solution is to see what is discharging from the trap. Through a combination of some piping changes and valves and nipples, you can install EVERY F&T trap with its own test station. The added cost of a few nipples and a valve is offset by the ability to troubleshoot the trap later.
Why should I install the circulator on the supply side of the boiler piping? I have always installed them on the return and they worked fine!
It is true that most small, residential circulators will work OK when they are installed on the return. It is also true that the system will operate better/more quietly/possibly more efficiently when the circulator is installed on the supply. What’s important is to know what happens when a circulator turns on and how it affects the system’s static pressures. When you locate a circulator on the return, it is “pumping” towards the system’s expansion tank. And the expansion tank’s connection to the system is called the “point of no pressure change.” Therefore, the circulator’s pressure differential cannot change the pressure at the location of the tank.
Of course, the circulator still has to create a pressure differential across itself, but since the discharge pressure can’t change, the pressure on the suction side drops. With small residential circulators, the pressure differential is low, so the static pressure is lowered slightly.
But with larger circulators, the differential can cause the system’s pressure to drop below atmospheric pressure (vacuum) and create all kinds of air/noise/gurgling problems. Why not locate the circulator in a place in the system where it is working for you, instead of against you?
If you have any questions or comments, e-mail me at gcarey@fiainc.com or call me at FIA. 1-800-423-7187 or follow me on Twitter at @Ask_Gcarey
uld run to satisfy the building’s heating needs.
1) High pressure steam moves faster
In a hot water heating system, to provide heat, we need to move or circulate heated water from the boiler out to the radiation. Years ago, before circulators, the pipefitters used gravity to distribute this heat out to the radiators. By using oversized pipes, which offered very little resistance, the buoyancy of hotter, lighter water and some fancy piping techniques, the old timers successfully circulated water around the heating system. Once circulators came on the scene, gravity installations were discontinued almost immediately.
Because the electric motor and impeller created the motive force to circulate the water, it wasn’t necessary to use the oversized pipes. You see, whether you are talking about an old gravity system or a modern hot water system, the ONLY way to get the heat out of the boiler and into the radiation is by circulation.
And what causes circulation? Years ago, they used the difference in the weight of hot versus cold water. Now this certainly doesn’t create a large motive force—hence the oversized pipes, which created very little resistance or pressure drop. Today, we use circulators to create this motive force.
But why does the water need help in moving at all? Why can’t it just flow out to the radiation?
FRICTION! As the water flows through the pipes and the radiation, it “rubs” along the interior surface of these items, and this “rubbing”action creates friction or resistance. So energy is “added” to the water each time it passes through the circulator’s volute.
A common term in the industry is “feet of head.” It is used to describe how many feet of head energy are added to the water by the circulator. The answer, of course, depends upon the specific flow requirements needed in that particular system and what the frictional resistance is at that flow rate.
Another interesting aspect that occurs is the fact that all of the head energy added to the water at the circulator is consumed by the system. This means there is no “leftover” head energy. The circulator will strive to move as much water (expressed as gallons per minute or GPM) as it can, limited only by the amount of head energy added to the water by the electric motor and impeller. And whatever that amount is, the frictional resistance offered by the system will consume all of it.
I received a phone call from a very frustrated contractor who had just installed new equipment in a boiler room upgrade. The upgrade included a new, high efficiency boiler, new indirect water heater and circulator and also a new system distribution circulator that provided heat for the entire building. His source of frustration was coming from the fact that the DHW circulator could not operate anytime the main system circulator was running. And the main system pump was designed to operate 24-7 once the outdoor temperature dropped below 65°F. He had the potential of having a building full of warm but smelly tenants…Not good! He was thinking the bigger main circulator was “too strong” for the smaller DHW circulator, which he thought kept that circuit’s check valve back seated because of the larger pressure differential developed by the main circulator.
I appreciated where he was coming from—high head circulator pumping right next to a smaller “headed” pump; but you have to remember that as the water flows throughout the system and is “rubbing” along the walls, the head energy is dissipating…so much so that by the time it has returned to the suction of the pump, all of the circulator’s pressure differential is gone. That is why you can have several different sized circulators sitting next to each other on a manifold and they can all co-exist without negatively impacting one another. Of course, the manifold needs to be properly sized or even better, oversized to allow this to occur.
Figure 1 (CLICK TO ENLARGE)
I was involved with another job where Delta P or pressure differential was creating the problem. In this case, the complaint was unwanted heat in a zone that was off—the thermostat was not calling and the respective zone valve was CLOSED! The job was piped like the drawing in Figure 2. As you can see, the system was zoned with zone valves on the supply header down in the boiler room and the system circulator that served all of the zone valves was on the return line, pumping back towards the boiler. The service technician who had called me tried to describe over the phone how it was piped and what was happening. A top floor unit was overheating so badly that the tenant had the thermostat turned down as low as it would go, had windows partially open and it was still 77-78°F in the unit.
Figure 2 (CLICK TO ENLARGE)
With the cost of energy on everybody’s mind, it would be wise to provide your customer with a hot water heating system that operates efficiently. One area in particular that has gone on unnoticed is short cycling, which is an efficiency destroyer. And it can hit in two areas: mechanically and economically.
The mechanical problems will occur because of the rapid on/off cycling of the boiler. All of the various components found on an oil-fired boiler have an expected life cycle. When a boiler is short cycling, the components are seeing all these cycles in a very short time span. This leads to premature control failures, nuisance lock-outs, service calls and frustrated customers. If you want to destroy a brand new boiler in a short period of time and frustrate your customer along the way…short cycle it!
The economical problem is often unknown and certainly under-appreciated. There is an old rule of thumb that states, “A short cycling boiler will operate at least 15% below its rated efficiency when said boiler is not short cycling.” The loss of fuel efficiency can be staggering. That means the wasted fuel consumption is paid for by the unsuspecting homeowner with the new high efficiency boiler.
So if you want to prevent short cycling, what can you do? The first step is to ensure that the boiler is not oversized! When a boiler is too big, it will always produce more energy (BTUs) than the system needs. And by being too big it reaches its high limit very fast, a condition that does not allow the boiler/burner to operate in a “steady state fashion”. And the best way to make sure that a new boiler is not too big is to perform an accurate heat loss on the house. There are several software heat loss programs available that will help you establish the heat loss of any building. By using this information, you can then select the right size boiler for the house instead of using the “looks a lot like” method or the famous “read the label on the old boiler” method.
Unfortunately, as the expression goes, “…no good deed goes unpunished.” A boiler can still short cycle even when it is sized properly. Do you know why? Load and zoning are the reasons. A properly sized boiler is sized for design conditions. This means when it is very cold outside (design outdoor temperatures), the boiler is capable of keeping the occupants at design indoor temperatures. But these design outdoor conditions exist for less than 5% of the total heating season. Which means for the remainder of the heating season, even the properly sized boiler is too big and can possibly short cycle.
One of the many advantages and selling features of hydronic a system is their ability to be zoned very easily. Most homeowners like the idea of being able to control sections of their house, even right down to a room-by-room control. But this, unfortunately, can also lead to short cycling. If one or two small zones are calling and the boiler fires in response, the energy output of the boiler is too great compared to the needs of the smaller zones. In that case, the high limit is reached very rapidly and the boiler shuts off. The zones continue to call and the water temperature drops, the limit control responds and the boiler fires up again. Of course, the high limit is again reached quickly and the boiler turns off. So even though the hydronics industry promotes zoning capabilities, and homeowners enjoy the comfort and control offered by zoning, it can impact a boiler’s potential operating efficiency.
If you were to ask any boiler manufacturer what would be an acceptable firing on-time that would eliminate short cycling and all its downfalls, a minimum of 10 minutes “on -time” would be the answer. So what can we do to achieve this 10 minute firing “on-time”? Here are a couple of ideas:
One would be to improve the controlling operation of the system. And a system it is…for a long time we have allowed the individual zones to operate independently and therefore, randomly. The net result is inconsistent and very uneven loading of the boiler, which often leads to harsh boiler short cycling. Granted the occupants upstairs are still relatively comfortable but at what expense? There are thermostats available on the market today that synchronize with each other (i.e., they talk to each other). By synchronizing, they all call for heat at the same time at the beginning of each new heating cycle. Naturally, how long each one runs for is determined by that particular zone’s needs. The benefit of this is the boiler is seeing a reasonable load/flow rate that it can work with, thus minimizing the short cycling.
Another benefit of these “new thermostats” is they also can request a water temperature back to the boiler control. The control receives these requests from all the various zones and makes a decision based upon the zone with the highest temperature requirement. The other “lower temperature” zones then calculate their own on-time with the higher temperature water to maintain their desired setpoint.
The other option would be to provide some mass to the system so that each time the boiler fires, it would have to raise the temperature of this mass X number of degrees. If the added mass is calculated correctly, the boiler would not short cycle! This added mass is known as a “Buffer Tank.” So how much mass is needed? How big should this Buffer Tank be? It is actually a rather easy number to establish. It is based upon a couple of conditions:
1) the minimum firing on-time of the boiler (usually 10 minutes);
2) BTU/H output of the boiler;
3) the minimum btu/h load of the smallest zone calling and
4) the desired/acceptable temperature rise (delta T) of the tank (usually 20-40 degrees F).
When you plug in all the necessary numbers, the answer will be the suggested size of the buffer tank in gallons. For example, if we had a boiler with a Btu/h input of 150,000 and the smallest zone load was 5000 Btu/h and the system could accept a 40°F rise, what size buffer tank would be needed?
In this particular system, with a 72.5 gallon buffer tank and the smallest load calling, the boiler would run for a minimum of 10 minutes and operate more efficiently.
Some might say that the additional cost of the tank would be prohibitive, but when compared against the life of the system, the cost of energy and the efficiency points gained by the longer “on-times”, I think the benefits outweigh the additional equipment costs.
If you have any questions or comments, e-mail me at gcarey@fiainc.com or call me at FIA. 1-800-423-7187.
Recently, steam systems with problems—for whatever reason—have been coming at me fast and furious. I have been receiving phone calls, emails and called to jobsites with steam systems that are experiencing all kinds of problems. I have noticed though, with all of the jobs, there is one constant—the guy or guys solving (or creating) the problem really didn’t understand the nuances that a steam system brings to the table. I’m talking about such things as the fact that:
In addition to looking at these problem steam jobs, I have also been writing stories about and designing hydronic systems that use Air to Water Heat Pumps.
Many in the industry view these machines as “State of the Art” technology. Their compressors incorporate invertor technology which, in the “compressor world” is state of the art. The invertor basically allows the compressor to operate like a variable speed pump, and the expansion valve can operate over a wide range of loads, allowing the heat pump to extract heat from lower outdoor air temperatures than was previously possible. But at the end of the day, for any of these air conditioners and heat pumps to work at all, it all comes down to the vapor compression refrigeration cycle.
What does this have to do with an article about steam systems with problems? If you understand the vapor compression cycle—and IF you understand what a steam system is trying to accomplish—both systems have similar attributes.
Here is what I mean…
To make steam, the boiler HAS to heat the water in the boiler up to the water’s boiling point. What is the boiling point? It depends on what pressure the system is operating under. When a steam system operates under higher pressure, the water’s boiling point is higher. Also the temperature of the steam is hotter.
Two types of heat
Now, when I say the boiler has to heat the water, there two types of heat needed to make steam. Sensible Heat is the type of heat that a thermometer can sense. For example, when the boiler is operating at 2 psig, the boiler has to provide enough sensible BTUs to heat the water to 219°F.
The other type of heat is known as Latent Heat. This is the amount of energy (BTUs) that is required to change the water’s state from liquid to vapor. Why? Remember, we are dealing with a steam system. For it to work, you HAVE to change the water into vapor. So in our example, the boiler would have to add an additional 966 BTUs of latent heat per pound of steam. That is five times greater than the amount of sensible BTUs that was needed to bring the water to a boil under 2 psig. Now when this 219°F steam travels out into the system and fills a radiator, it condenses back to water. And the temperature of the water can be 219°F, but the radiator has received 966 BTUs that it uses to warm the room.
When any medium goes through a phase change, it will either be absorbing or releasing a tremendous amount of energy. And that is how I was drawing a parallel between the vapor compression cycle and steam systems. In the compression cycle, instead of water, refrigerant is used which has many favorable characteristics for the refrigeration process. It can operate under extreme temperature conditions (extreme relative to what we consider normal); it can also change state and go from a liquid refrigerant to a vapor and then condense back to liquid, all the while absorbing and releasing energy (heat) to where it’s needed (as a heating application) or from where it is not wanted (as in an air conditioning application).
Of course there is no boiler in the refrigeration cycle. Instead, an evaporator is used to help change the refrigerant’s phase and the compressor is used to increase the pressure on the vapor, resulting in a high temperature gas.
Before the vapor enters the compressor, it first flows across the evaporator as a cold liquid refrigerant. The volume and temperature of the cold liquid is controlled by an expansion valve. Outdoor air, or some other substance (such as geothermal) is flowing across the other side of the evaporator. The cold liquid absorbs the heat from the outdoor air (or geothermal field) and changes its state into a low temperature vapor.
To prevent damage to the compressor, it is critical that only vapor and NO liquid enter the compressor. The low temperature vapor gets “compressed” into a high temperature gas that now flows across a heat exchanger. The cooler medium (return air from the ductwork or water from a hydronic system) flows across the other side of the exchanger. This cooler substance (air or water) absorbs the energy from the vapor, causing it to condense back to its liquid form. In the condensing process, a tremendous amount of energy is transferred.
When we take it back to our steam heating systems, the boiler is our evaporator—and to some extent—our compressor. Its job is to add enough sensible AND latent BTUs so that the water is changed into steam (vapor). When the steam enters the radiator, its surface and surrounding air temperature is cooler than the vapor (steam) causing it to condense back to water (liquid). In doing so, it gives off a tremendous amount of energy (BTUs) to the space.
So how does analogy help solve or prevent steam system problems? Make sure the boiler is making good, DRY steam. When it makes wet steam, the water in its liquid state “robs” the vapor of its latent BTUs. When this happens, the steam is condensing in the piping network and NOT where it’s needed…in the radiators!
How do we make good DRY steam? Make sure the new boiler is piped according to the manufacturer’s installation instructions. Do what they say!
A bouncing water line in the boiler can also make wet steam. If the water is moving in the gauge glass, it’s an indicator that the water in the boiler is dirty. It needs to be skimmed to rid the boiler of any oils and debris that cause surface tension on the water, prohibiting the steam bubbles from making their way through the surface and out to the system.
When a boiler is undersized or underfired, it can’t produce enough steam to fill all of the radiators. The condensor side of the system (the radiators) is bigger than the evaporator side (the boiler). It is imperative that when you replace a steam boiler, go upstairs and measure the amount of radiation in the house (apartment, school, church, etc…). Then size the replacement boiler to the connected load.
Whenever you are dealing with a steam system, it is vital that the boiler is making DRY steam. If it isn’t, don’t waste your time chasing other symptoms or complaints…ALWAYS start with DRY steam.
If you have any questions or comments, please email me at gcarey@fiainc.com or call at 1-800-423-7187.
As the heating season approaches, the landscape, with regards to residential and commercial mechanical rooms, has drastically changed. Over the years, when you entered a typical boiler room somewhere up here in the Northeast, it was very common to find a sectional cast iron boiler or boilers and usually some type of indirect heating appliance for domestic hot water. It could be a side-arm heat exchanger with a storage tank or a storage tank with the heating coil installed directly inside. Nowadays it has become “almost the norm” to walk in and find very highly efficient modulating and condensing gas-fired boilers (either LP or Natural). These boilers are not your average “run of the mill” atmospheric gas boilers either, because their efficiencies range between 90 to 96%. They use a Neg/Reg gas valve and fan assembly which means the amount of gas that flows into the burner for combustion is regulated by the fan assembly’s blower speed. The blower speed is controlled by an onboard micro-processor that is performing several internal calculations to determine the appropriate amount of BTUs needed to satisfy the call. Hence the modulating part…it only uses the amount of gas necessary to satisfy whatever load it is currently “seeing”.
Most of the residential models have a “turn down” ratio of 5 to 1, meaning they can fire down to 20% of their total capacity and, of course, all the way up to 100% of their capacity. It has become quite common in larger residences to install two or more smaller “mod/con” boilers that, when combined, can handle the home’s total load. But more importantly during the normal course of the heating season when the home is operating at part load, the boiler plant consumes just the amount of energy needed to satisfy the current load the house is “seeing”. The same holds true for commercial applications such as apartment buildings, condominiums, churches and schools.
The larger commercial “mod/con” boilers offer turn down ratios up to 10 to 1. That means with a couple of commercial boilers, you can fire down to 5% of the total BTU capacity of the boiler plant! With this type of turn down, building owners are experiencing fuel savings in the range of 35–40% and higher!
Another unique feature with these boilers is the venting options. The blower motor is designed to not only Opportunities this heating season… bring combustion air into the burner assembly but also vent the residual products out of the building. Most of the “mod/con” boiler manufacturers have approved their boilers to use several different vent materials. They are approved to be vented with PVC, CPVC, polypropylene and stainless steel vent pipes. Each manufacturer provides very detailed instructions on the “Do’s and Don’ts” regarding how to properly vent their boilers. Following these instructions is critical to allow the boilers to operate efficiently. Naturally, all of this piping needs to be sealed tight to meet the venting codes.
So where is the opportunity?
These boilers encourage the condensing of their flue products, which is the exact opposite of traditional boilers. Their heat exchangers are designed to withstand the corrosive nature of the condensate that forms when the combustion products are condensed. Of course, this condensing action is where the additional efficiency points are obtained. Some of the byproducts of this condensing can gather upon the boiler’s heat exchanger. If allowed to accumulate, they will negatively impact the boiler’s efficiency performance, which is why the manufacturers all suggest an annual inspection and cleaning of the heat exchanger, if necessary. Also, the venting should be inspected to make sure nothing has changed that could interfere with the operation of the boiler.
This means EVERY “mod/con” boiler NEEDS to be inspected each year. One of the oil industry’s shining stars has been their reputation for service and maintenance. The need for these high efficiency boilers to be maintained is a perfect opportunity for a company that has a service department to offer service contracts to home owners and commercial property owners and management companies. Most of the boiler manufacturers or their local representatives offer classes on servicing these new “mod/con” boilers, which I strongly suggest attending.
What else?
A new style of “smart” pump is making its way into the North American hydronics mechanical rooms: ECM pumps. ECMs (electronically commutated motors) are very different from the PSC (permanent split capacitor) motors we have been using in our wet rotor pumps. This new style motor is sometimes called a “brushless DC” motor. The rotor in ECMs have permanent magnets, instead of wire windings that are separated from the system fluid. The magnets are located inside a stainless steel rotor container and react to the magnetic forces created by electromagnetic poles in the stator.
A microprocessor which “sits on board” the pump reverses the polarity of the stator poles rapidly (within milliseconds), forcing the rotor to be rotated in the proper direction. The faster these poles reverse their polarity, the faster the rotor spins, meaning the faster the impeller spins.
ECM circulators can provide four times more starting torque compared to a PSC wet rotor pump. This additional starting torque pretty much eliminates the concern of a pump experiencing a stuck rotor after a summer shutdown.
ECM pumps incorporate a microprocessor that has software on board allowing the pump to perform many functions. For example, one application may call for a constant pressure differential where the building is partitioned with zone valves. Normally, as valves close, the pump would develop additional head pressure across the remaining open zones, causing an increase in flow rate through these zones. This wastes energy as well as creating potential noise problems due to increased velocity. With a constant differential in pressure capability, as valves close, the pump momentary senses an increase in differential pressure and quickly slows down the pump’s speed to eliminate the change in pressure. The result is no change in flow rate through the remaining open zones, no wasted energy and no velocity noise problems.
Another application that the microprocessor can control is called proportional differential pressure. The circulator control is set for a specific design head loss for a system. Now when the zone valve (or valves) closes, once the pressure differential starts to climb, the circulator reduces its motor speed. The difference here deals with proportional control; instead of maintaining a set differential, it will lower the speed and thus cause a pressure differential proportional to the reduction in flow rate. The result is an increased reduction in energy consumption.
The efficiency of these “greener” circulators is designed to meet the ever increasing efficiency standards that are slowly making their way over to North America. The “wire to water” efficiency these circulators have are higher than the current PSC wet rotor circulators. The multiple application capabilities, with the on-board microprocessors, as well as the reduction in wattage use make ECM circulators very compelling alternatives to the industry’s current offerings.
You should become aware and comfortable with this newer technology.
If you have any questions or comments please call me at 1-800-423-7187 or email me at gcarey@fiainc.com.
