A number of months ago we were approached by a church and given the opportunity to develop a hydronic heating solution for their main sanctuary and meeting area. The existing system that served the church was a 1.5 MILLION BTU cast iron boiler. To put that in perspective it's about 15 - 20 times larger than a furnace found in most residential homes. That is also a measure of how much natural gas it is designed to burn, not how much heat it actually delivers to the space. Even if we assume 70% efficiency (which might still be generous) it's over 1 million BTUs of heat being generated by this beast. I think it really earns that name too, I mean, just look at the thing:
To give you a sense of scale, that's a 6 foot ladder you can barely see behind it and I think that's a 12 or 14 inch exhaust pipe you're looking at. It even has an angry face from the other angle:
We're pretty sure this was original to the building, a suspicion that was confirmed when removing it we discovered the concrete floor was actually poured AROUND it! So, after it was removed and the hole patched appropriately, it was time to replace the Beast with something a bit more modern and efficient, but what to use?
We began this project as we do any other, by conducting a survey of the building and calculating the heat loss using the Manual J calculation. As I said before we were serving the sanctuary, narthex, organ loft, and basement as well as replacing another small boiler that served a new entryway on the back of the building. I'm sure at some point in the past someone much have thought 1.5 million BTUs seemed about right for a building of this size, but I wasnt' sure. The very conservative heat load (no one really seemed to know how much, if any, insulation was in the walls between the plaster and the brick, so I assumed there wasn't any) revealed that the total heat load for the entire building was 400,000 BTU/hr. Remember that include the new entryway with lots of windows that added over 75,000 BTU or heat itself and that 400k is on the coldest day of the year. Needless to say, "The Beast" was extremely oversized from day one and had been consuming far more than his fair share of gas the entire time.
Gas wasn't the only resource being consumed more rapidly than it needed to be, though. The old system used modulating valves to control the amount of heat and the rate it was delivered to the spaces. I was actually impressed by this arrangement and in theory it should provide very even temperatures. The valves were opened and closed by thermostats that sent an electrical signal that varied depending on how far away the set point was from the actual temperature. I'm not sure exactly how it was configured, but if you can imagine the sanctuary was 65 degrees and you wanted it to be 66, the valve would open a little to heat it up a little, but if it was 60 degrees and you wanted it to be 65, it would open a lot (or all the way, probably) to warm up as quickly as possible until it tailed off the closer it was to the setpoint. Not bad as far as comfort control is concerned for a 50 year old system.
There was a problem, though. The pumps for the system ran continuously. They were actually on lightswitches and would run from roughly October to March every year. 24/7. That doesn't seem like it would be a huge deal until you start to do the math. These were larger commercial ciculators - I'm pretty sure some were larger than others, but we'll be kind and assume they were all of the 1/6 HP variety with an amp draw of 2 amps. I'll spare you the math (See the bottom of this article if you want to see it worked out) but it works out to - near as makes no difference - $120 per year. Per pump. and there were 4 of them. So, $480/year was being spent just to run the 4 circulator pumps continuously for 6 months.
Needless to say, there was plenty of opportunity to improve on the efficiency side of the equation for the church, but we wanted to make sure we were putting together a system that was reliable and effective as well. The initial plan involved three smaller modulating-condensing boilers similar to what we had put in our own shop when we built it. The idea was to apply the KISS principle and two of the boilers would simply supply the two largest areas of the church - one for the sanctuary that had radiant floor heat and would use lower temperature water, and another for the basement that would use high temperature water for the fin-tube wall radiators. The third would be the "complicated" one and serve 3 lower temperature zones and the indirect domestic water heater.
This is actually the concept we were planning on using until our vendor suggested we consider doing a cascade of two larger boilers rather than 3 independent systems. The cascade system would simplify some aspects of the install while complicating others, but brought with it some very tangible benefits. I should first explain what I mean by a cascade system. A cascade of boilers is simply multiple boilers that are connected to the same piping system and controlled in such a way that the capacity of both are able to supply heat to the space as well as provide redundancy for the boilers. The cascade controller handles both; bringing on enough boiler capacity to meet the heating demand as well as making sure both boilers are used an approximately equal amount of time as well as allowing a fail over if one should stop working.
The largest complication of switching to a cascade system vs the independent boilers was the different temperature zones we would need to have. The majority of the zones are low temperature radiant floor heating, but the lower level has radiators and the indirect water heater that need hotter water to work correctly. That problem was solved through the use of mixing valves that take the high temperature water produced by the boiler for the radiator zone and mixing it with water returning from the zone to make the water the lower temperature needed the radiant floor zones. We used 4 individual mixing valves so we could adjust the zones independently to balance heating capacity with comfort.
In addition to the mixing valves and cascade control, the system had two other controls that help maximize efficiency and flexibility of the system while remaining very simple to control. The first is the outdoor temperature reset control. In a nutshell, it changes the temperature of the water produced by the boilers based on the outdoor temperature and by association the heat load of the building. Lower water temperatures means the boilers don't have to get as hot and allows for maximum condensation of the flue gasses, maximizing boiler efficiency. That works great for allowing the boilers to make 140 degree water to send to the radiators when it's warm outside, but that doesn't work very well for making 120 degree water in the indirect water heater. That problem is solved by the cascade controller and the next control, the Enhanced Switching Relay, or more simply, the pump control.
The pump control takes the input of the thermostats from around the building and brings on the appropriate pumps and sends a signal to the reset control that it would like heat. The reset control takes that signal, determines what temperature water it would like from the boilers and sends it on to the cascade control that determines which boiler to bring on and at what firing rate to satisfy the temperature requirement from the reset control. Let's simplify that a little:
Thermostat > Pump Control > Reset Control > Casade Controller > Boilers
As more zones come on, but boilers adjust their firing rate and even bring on both boilers to try to get to the temperature requested by the reset control. This all happens automatically, and at any given time there is exactly as much heat being produced as needed and it is doing so as efficiently as possible. But what about that water heater I mentioned earlier? Doesn't it throw everything off? After all, you don't want to try to heat 50 degree incoming water to 120 degrees using 140 degree water - it would get there eventually, but it would take forever. Something I forgot to mention, the reset control won't even let the boiler come on if it's more than 70 degrees outside.
So does that mean no hot water in the summer? No, we've got a little trick up our sleeves. You see, the pump control has a special priority zone that we can hook the water heater up to. When the aquastat on the water heater says it needs heat a few things happen. First, the pump to the water heater turns on and the other zones turn off - that is the priority part - it jumps to the front of the line. The pump control also has a priority output that connects directly to the cascade controller - bypassing the outdoor reset control and brining the boilers on at high fire - producing 180 degree water for as long as the water heater needs it. So to recap, it looks like this:
Aquastat > Priority zone control > Cascade controller > Boilers
This arrangement allows us to make hot water very efficiently and in very large quantities.
Some of the other efficiency and performance features of the system are the thermostats and the pumps. The thermostats are internet connected and allow for system monitoring, adjustment, and scheduling remotely. They will also send an alert to email addresses if there is a power loss, high or low temperature problem or any number of other conditions that can be set in the system. The pumps are also special - they aren't simply fixed speed pumps (with the exception of the indirect water heater) but rather vary their speed based on the temperature difference between the supply and return water and get as close to 20 degrees as possible. That means that the pumps are able to speed up or slow down throughout the heating call to get the zone up to temperature as quickly as possible (by flowing more water initially) and then slowing down as the pipes heat up to minimize energy use and maximize comfort. Where the old pumps used over 240 watts to run, these pumps, that only run when there is a demand, only use about 40 watts at the most and run even lower as conditions allow. The pumps alone should save over $400 a year in electricity.
So I titled this entry Beauty and the Beast - we've already met the Beast - and while I think the new system and its installation is a thing of beauty, the real Beauty is the savings that will be achieved by this system. By using available technology, properly sizing the system, and designing intelligently to maximize efficiency, effectiveness and reliability the church should see tremendous gas and electrical savings vs the previous system. Maybe some day I'll be able to post a follow up to this, but I wouldn't be surprised if the savings approach 50% and that, my friends, is a thing of beauty.
2 amp x 120v = 240 watt per pump
240W x 24 hr/day /1000 = 5.76 kWhr/day/pump
5.76 kWhr/day x 180 days/year = 1036.8 kWhr/year/pump
1036.8 kWhr/year/pump * $0.115/kWhr = $119.23/year/pump
4 pumps x $119.23 = $476.92 ~ $480/year pumping cost.
Almost a year ago we began planning the HVAC system in our new office and had to decide what we wanted to do. We knew we didn't want to do the "normal" of a forced air heating and air system as that is what we were coming from and recognize the shortcomings of that system. Even with a heat pump and zoning we found ourselves constantly fighting the temperature in the office and it was not particularly efficient overall. We also didn't have an unlimited budget, so we had to balance comfort, efficiency, Indoor air quality and price.
In the end we decided on radiant heat in the concrete slab floor of the offices, a hanging heater for the warehouse area (to keep it above freezing mostly), and mini-split heat pumps in every office space. If a customer wanted to have the best comfort and efficiency, this is the direction we would point them as well.
The radiant floor heat will provide a very even baseline temperature throughout the office (and keep our toes warm). The thermostat controlling the system has a floor temperature sensor and an air temperature sensor to make sure we're keeping the slab warm without overheating the air above it and making sure the floor maintains at least a minimum temperature throughout the heating season.
The mini-splits are part of a heat pump system, which means they can both heat and cool the space they are in. In the cooling months, they provide precise, quiet, and efficient cooling to each area. That means that when Tom wants his office 65 degrees he can do that without making everyone else cold. When Pat doesn't want any cooling in her office, she can do that too. In the winter, we have the heated floors providing a baseline temperature for the entire office while the ductless units take care of fine-tuning the temperature in every room above the heat the floors provide.
Every single space having its own temperature control takes a little getting used to. Just like you would turn a light off when you leave a room you don't intend to come back to or aren't using we try to simply turn the system off when we leave for the day or in the case of a conference room on turn the system on only when it is used. Between the super insulated and air sealed exterior and the quick recovery of the system the room can be made comfortable in matter of minutes. After a few months it looks like the new building will cost the same or less than the old building that was one third the size.
Speaking of the building, lets talk about its role keeping us comfortable and minimizing the monthly energy bills. The building is a pole framed building over an insulated concrete slab. The exterior walls and the underside of the roof deck were sprayed with at least 6 inches of open cell foam insulation. When combined with the steel siding and roof and the house wrap below it, things are very tight from an air leakage perspective.
With that tightness in mind we wanted to make sure we didn't forget the "V" in HVAC - ventilation. The last thing we want is a temperature controlled Petri dish - we want to make sure we have a way to bring in fresh air and exhaust the stale. To that end, we have an Energy Recovery Ventilator. This unit takes in air from one end of the building, exhausts it outside and brings in fresh outside air to the other side of the building. This isn't just like opening a window, however. Both air streams pass through something called an enthalpy core where they exchange their heat and humidity. That means that in the hot summer we don't just send out nice cool and dehumified air and bring in hot humid air. Instead, the ERV moves most of the heat and humidity from the incoming air into the air leaving the building. That way we get the best of both worlds - fresh air and energy savings vs. just bringing in outside air unconditioned and "throwing out" nicely conditioned air.
Overall we've been very happy with the system and being able to set your own temperature is a nice luxury to have. We'll see what the cold weather brings, but we have every reason to believe the choices we've made will allow us many years of trouble free comfort. Check out the gallery below for even more pictures.
I thought I would put together a quick post to provide some education about the problem of letting your dog (or your neighbors' dog) urinate on your air conditioner. Besides being pretty gross, it's also doing serious damage to an expensive piece of equipment that you rely on to keep you cool when it's the hottest. The urine will actually eat away the aluminum fins on the condenser coils until only the copper lines remain and more than likely a leak or two or three will develop. You'll end up replacing the condenser sooner than you should have to and the dog's not going to help pay for it!
Don't believe me? I present exhibit A
Yes, we had to replace the unit. It's easy to see on this unit, but if you've got coil that you can't see and dogs that aren't thoughful, check to see if you've got damage and put a stop to it!
Stay cool this summer, even during the "Dog Days" !
A while back I posted about the problems many homeowners face with regard to areas of their homes that they simply aren't able to use very much they're not able to keep them at a comfortable temperature. I have a confession to make: I am one of those people -- or should I say, I was. I don't have a 4 seasons room, or even a 3 seasons one. I have a bonus room.
Bonus rooms, or my favorite acronymn used to describe them F.R.O.G (Finished Room Over Garage), are a somewhat newer phenomonon, but the concept is ages old: convert what would otherwise be unused and unconditioned space over a garage or other portion of your home into "living" space by insulating, drywalling and adding some kind of HVAC into it. My FROG is above the garage and is approximately 10 feet by 20 feet with sloped ceilings and a window at the end. With a young family we have turned it into a play room for the kids - an area of the house that the toys can live so we have some hope of keeping the bedrooms and other living areas approximately clutter free. There was problem, though - it was almost completely unusable because of the temperatures in the space.
When we first moved into our home we had a single furnace and air conditioner that served the entire home through a single duct system with a single thermostat located in the living room on the main level. There was a single 10 inch round duct that ran from the furnace into the attic where it split into a ductopus to serve the three kids' rooms, a bathroom, and bonus room. Thankfully we moved in late summer because the kids soon had relief from the 80 degree temperatures that were the best we could achieve when the days were warm. The solution for the kids was to increase the size of the trunkline to the second floor and add a zoning system with a thermostat located on the second floor. By adding the ability to sense the temperature on the second floor and direct cool (and warm) air there as needed we had reclaimed that living space (or at least didn't have to feel guilty making our kids sleep up there). The bonus room, however, didn't fair as well.
You see, for the most part, bonus rooms like their 3 and 4 season room breathren exist as a bit of an appendage on a home. As a result they are literally surround by heat load or loss surfaces that lead to wildly different heating and cooling requirements than anywhere else in the house. Think about this for a minute. The room you're sitting in right now more than likely doesn't have more than 3 surfaces that are losing heating (or gaining it, depending on the season). You probably have a wall or two and then either a ceiling or a floor that is touching the great outdoors or otherwise unconditioned space (attic, garage, etc). The rest of the walls, floors, and ceilings are likely shared with other rooms or conditioned spaces and represent no heat loss or gain in the room. So, when we have a bunch of these rooms touching each other and none of them has a terribly large loss or gain we can usually stay pretty comfortable with a single thermostat and a single duct system.
However, a bonus room has almost all of its surfaces touching the outside world. In my case I have a door and about 10 square feet of wall that is shared with my daughter's room. The rest is a floor over the unconditioned garage, walls that are touching a vented knee-wall attic, ceilings with the same, and a window to top it all off. What had the builder of our home done to accomodate what is a heat load and loss wildly different than the rest of the second floor? Two supplies of 6" flex that come out low on one of the walls and a single return. At least there is a return. Needless to say, it isn't nearly enough and even if it were, the system only runs when the 2nd floor thermostat calls for heating or cooling.
So, what's an HVAC guy to do when faced with a comfort challenge in his own home? I took my own advice and installed a ductless mini-split system. A ductless system is really the perfect fit for my application. I have a finished area that has wildly different heating and cooling loads that the adjacent areas, but it isn't really all that large an area that would require a completely seperate furnace and air conditioner. The model I chose to install is the Mitsubishi FE09 Heat pump. The system consists of an inside unit that mounts on the wall and an outside unit that houses the compressor. I chose to open up the drywall and run the refrigerant lines, drain, and control wiring inside rather than outside which made the project take a little longer but will result in a very high WAF (wife acceptance factor) when everything is done. The system is extremely efficient and provides both heating and cooling. Because it uses a variable speed compressor, the unit only runs as fast or slow as it needs to achieve the temperature. As a result the unit is also extremely quiete (watch this space for a video comparing this unit to our whole-house air conditioner).
The resuls of the project are almost unbelievably comfortable temperatures in the bonus room and we now have a space that we can truly use. We can now say that we have extra space that is a "Bonus" rather than a hot or cold room that we happen to store the toys in. Check out the pictures below for how it all turned out.
We can see the light at the end of the winter tunnel. There is still a little bit of snow on the ground from last week, but the warmer weather and rain from the weekend has almost erased all signs of winter from the landscape. The brown grass is just about the only evidence this isn't a late spring or early fall morning. So why am I thinking about heat exchangers? Well, we've been dealing with a lot of them recently and it has become obvious to me that there is a lot of confusion and misinformation when dealing with this subject.
As a homeowner, getting the news that your heat exchanger is cracked is a bit of a harsh blow. It's not unlike a doctor telling you about the "C" word. You know it's serious and you know you need to do something about it. Some people choose to live in denial of the seriousness of a cracked heat exchanger. They observe that their furnace is running just fine and was doing so before we arrived and will most likely continue doing so after we leave. The reality is that their furnace may be presenting a very real danger to their home and family and they need to address it before something terrible happens.
I'm not going to say that every cracked heat exchanger is a life or death emergency and that it is spewing levels of Carbon Monoxide into your home that can cause sickness or death. I am, however, going to say that every single cracked heat exchanger does need to be replaced, either through a complete furnace replacement or changing out the heat exchanger. If I can go back to my cancer analogy, you would never expect a doctor to say "Yeah, we found some cancer, but it's really in a non-critical area and you're feeling just fine, so we're not going to do anything about it. Go on living your life and we'll deal with this when it really becomes a problem." While you might not get rushed into emergency surgery to remove the offending tumor and surround tissue, you can be assured that there will be a treatment in your future. In the same way a cracked heat exchanger needs to be replaced, there is no repairing it and ignoring the problem simply isn't a solution.
So let's get back to basics for a minute here and talk about what a heat exchanger is and what it does. At its simplest level, a heat exchanger allows for the exchange of heat between two fluids without the fluids mixing. In the case of a forced air furnace, it is two different air streams, seperated by sheet metal or tubing that typically snakes back and forth to allow for the maximum amount of air to pass over it and the most heat to be exchanged between the two streams. Other types of heat exchangers exist in the HVAC world as well -- we can have refrigerant and air in an air conditioning or heat pump system, or air and water, like in a hot water boiler. The reason we want to keep the fluids seperate is obvious in the other examples - we don't want our refrigerant to leak out of an air conditioning system so we keep it within the coils and linesets and we don't want water leaking out of our boilers because that would be a hot mess. Why do we care about keeping the combustion air and house air separate in a furnace? What's the big deal, anyways?
Inside your furnace or boiler there is actually a fire burning, not unlike your oven. Natural gas or propane is being burned and the byproduct of that process is energy in the form of heat, along with varying amounts of water vapor, carbon dioxide, as well carbon monoxide, pure carbon (soot) and some Nitrogen Oxides (NOx). If you haven't already decided you wouldn't like those things to be in your house in any great quantities, let me tell you that almost none of them are desirable in large quantities in your home. With the exception of some additional water vapor in the home during the winter months, CO2, CO, soot, and NOx are certainly what I would call a pollutant and all of them can cause sickness or be fatal in high enough quantities. So why aren't we worried about ovens and stoves inside our homes? Two things - they aren't typically used enough or have a high enough output to worry about the levels they create and you're supposed to use a vent hood when you cook and bake. Everyone does that, right?
So why do heat exchangers crack in the first place? They're not supposed to, right? Heat exchangers are designed to provide safe operation of the furnace during its life expectancy - typically 15-18 years. However, there are many factors that can accelerate the wear and tear on a heat exchanger that they fail much sooner, sometimes in spectacular fashion. So what causes them to fail?
Sometimes it's just age and use. Where we live, furnaces see nearly 900 hours of use every winter. If we assume the average heating cycle is 15 minutes long, that heat exchanger is heating up and cooling down over 3,000 times per year. Try this experiment - take a paper clip, stretch it out and see how many times you can bend it back and forth before it breaks. So, sometimes heat exchangers just wear out with time and age and need to be replaced with a new furnace. Some times that's 15 years, sometimes it's 20 and sometimes they never crack and have other expensive repairs or the efficiency gain is enough to warrant replacment.
More commonly, the cause of a cracked heat exchanger is misapplication or poor maintenance of the furnace. All too often, furnaces are grossly oversized or used incorrectly which causes the heat exchanger to fail prematurely. Think of our paperclip example again. This time fold it completely in half for each "cycle" and see how many times you can do it. I promise you it will be far fewer times. When a furnace is oversized, a number of problems can exist including short cycling and cycling on limit. Both of those cause the heat exchanger to heat up and cool down far more often than if the furnace was closer to the proper size for the home or, better yet, was able to use a lower stage or modulate its heat output for smaller loads.
Another heat exchanger killer is airflow, or more specifically, a lack of it. The primary cause of low airflow in a furnace is a dirty filter. It can be hard to remember to change that filter or at least check it every month (which is why we recommend an air cleaner that can go for much longer without changing) If your filter gets clogged up with dust and dirt and the air simply can't get through, your furnace will cook itself to death. The heat simply won't be able to get out and the furnace will likely cycle on its high limit until it ceases to function or you change the filter. Meanwhile, your heat exchanger will go through a lot of stress when it is constantly overheated and cooled back down. Lack of airflow also leads to much longer heating cycles so not only is the heat exchanger hotter than it needs to be, it also has to endure the pain for a great time.
Sometimes it's easy to see the crack in the heat exchanger and understand why it's a problem, but what about when cracks are just forming or what if it doesn't seem like it's a critical area of the heat exchanger? It is our opinion and one shared by the American Gas Association (AGA) and AHRI that any crack, hole or other failure of the heat exchanger is reason to replace the heat exchanger or the unit. Sometimes the cracks like to hide like these:
But we can see why these are a cause for concern when we simply shine a light inside the heat exchanger and see this:
Our recommendation on finding a crack in a heat exchanger will always be to replace the heat exchanger or the furnace it is in because your family's health and safety is far too important to make guesses and assumptions about how dangerous this crack may or may not be. It's like the doctor that finds cancer - it might not be good news, but it needs to be shared and dealt with.
If you would like to have your furnace inspected and cleaned it's not too late in the season. Head over to our Specials page for money saving coupons too.