Heating a school house

[mbopo]

I am looking into relieving some of my wallet load for heating our remodelled 10,000 sq ft 1957 concrete block and brick school building/house. Yes, the indoor basketball court is cool, but most of the house is cold, despite a newer used propane boiler (270,000 btu) and better-than-baseboard radiant cove heaters. Every room we have remodelled has had walls furred out with 2x4's and insulation, but in december our boiler was going through $300 worth of propane in 5-6 days and our electricity bill was over $700. No, that is NOT sustainable. We really have only been trying to heat 6-8 average sized rooms (definitely not the basketball court!), but there is obviously some leakage into the unheated spaces like the hallway.

So my main question is - is there a way to utilize a GSHP system with the existing fin-tube heating system? Most GSHP's use water to water exchangers for radiant floor heat, or water to air using forced air systems I understand, but I won't install either of those if I don't have to. The suppliers tell me that i cannot connect the 2 directly together, as GSHP water is less than 140 deg and a gas-fired boiler has to be between 160 and 200 to avoid condensation of the products of combustion on the heat exchanger fins. I know I don't know much about all this, so any help would be great. I am an electrical contractor and jack of all trades looking to not spend $30-40,000 on a commercial system from which i will never live to see the payback. Trenching, plumbing, electrical and electronics are all DIY-able for me. Any ideas?

[Christian Nelson]

I would say you are having some SERIOUS heat loss. If you are only heating a few rooms, you should not be going through that amount of fuel. What kind of insulation are you using? I have found that quite frankly, fiberglass batting is all but useless. If air can get through it, it does nothing. I would do rigid foam, 4" worth on the inside of outside walls, giving you R-20. Your ceilings, do you have a drop ceiling? If so, those panels are not very insulating, and the air transfer between your rooms you are heating and the rest of the school building will be significant! WINDOWS!! Seal them up, make inside storm windows from plexiglass, etc.. Tremendous heat loss from the giant windows in some of these old school houses.

Once again, I would recommend at least R-30 on your ceilings. Look for air leakage. It's coming from somewhere! I've found the biggest factor is air leakage, same for mold, you get warm air meeting cold air, you get condensation. You cannot let the air leak.

Put rubber flaps on the bottom of all the doors to the rest of the building. Zone your heat, so you aren't heating the whole place, maybe even get a separate system for the areas yo want to heat all the time, and keep the rest of the building just above freezing.

Commercial school buildings were not built very well for heat retention (anyone who had to suffer through cold classrooms in school should remember this) the amount of heat they blow out on a constant basis is astonishing, only government would be able to throw that much on heating costs without doing somehting about it.

Anyhow, about the lower temp harming the boiler.. I disagree, I have baseboards, and with my boiler I have an outside temperature reset that sets the water temp lower if the outside air temp is higher. My boiler runs at around 120 through the fall, and many winter days, only when it is below zero F outside does it ever go above 160. Usually, it hovers between 130 and 150 for normal winter days. My home is cozy, and warm.

The things to especially look for in boilers is modulating valves, and outside temperature resets. Modulating valves make it so the boiler can come up to temp, and simply idle at the desired temp, rather than reaching temp, shutting off, and firing up full throttle. This uses FAR less fuel, and achieves a much more comfortable evnironment.

Your biggest thing to account for is getting a good heat loss estimate. slantfin.com has one you can download.

Then you can size the right boiler, and I see no problem with doing a heat pump. But the biggest things you need to worry about are heat loss, and cubit footage (I do not like using square feet, because you have a 3rd dimension you need to account for).

[Daox]

Hello and welcome to ER. I moved your post to get the attention it deserves.

I completely agree with Christian. You are loosing massive amounts of heat. You need to start with sealing and insulation. I would recommend even more than he recommended, but its a good start. It will definitely be more cost effective to insulate then upgrade the heating system.

[mbopo]

Of course, I can only agree with all the problems with heat loss that the building must have. We are putting R30 in the ceilings, replacing older windows with modern double-glazed low E etc and I am not sure what double block walls with an air gap plus 2x4 walls with R13 fiberglass insulation would be , but it seems it should be higher than the average house. I am sure that a lot of it is air leakage - however those issues will get more attention in the spring when it is less annoying to be outside and I should have the use of a thermal camera soon to check for the best spots to attack. Right now we have a temporary shower made of plastic sheeting, no tub, no laundry and no master bedroom. Kitchen/dining, living and kids bedrooms are nice and warm (but at a price). So I have, I am told, more pressing problems.
My main question is if I was to install a GSHP, how could I tie it into the existing boiler system which uses outer wall mounted fin-tube heaters. It would be a less than usual system, which is why I posted the question in the thread that I did - seems like there are several go-to guys on there not afraid to put systems together themselves.
My comment about suppliers saying that it shouldnt be run at or below 140 deg is backed up by the boiler manual and a federal government boiler how-to document produced for the military...140 seems to be the magic number. It was even recommended to run a controllable shunt pipe around the heating circuits which can be opened up to allow outgoing warm water to be recirculated back into the cold inlet water to ensure that the inlet does not fall below 140. Thankfully I have been able to keep that valve closed as I do not seem to have that problem. I know there are different types of boilers out there and it sounds like some can run below 140 inlet without problems, but i am leery to do this against the instructions from the boiler manufacturer.

[Christian Nelson]

My comment about suppliers saying that it shouldnt be run at or below 140 deg is backed up by the boiler manual and a federal government boiler how-to document produced for the military...140 seems to be the magic number. It was even recommended to run a controllable shunt pipe around the heating circuits which can be opened up to allow outgoing warm water to be recirculated back into the cold inlet water to ensure that the inlet does not fall below 140. Thankfully I have been able to keep that valve closed as I do not seem to have that problem. I know there are different types of boilers out there and it sounds like some can run below 140 inlet without problems, but i am leery to do this against the instructions from the boiler manufacturer.

It has to have run under 140, at the very least initial startup, and I am positive they do not expect you to run it all summer.

Most boilers have you do a bypass loop on the boiler to keep from shocking the heat exchanger. The problem isn't from running a low temp, but from the return water being significantly colder than the outgoing water, you can crack the heat exchanger that way, this is why they typically put a bypass, that mixes some of the exit water with the return before it comes back into the boiler. If you do not have a modulating gas valve, running lower temperature will simply have it short cycling alot, so it won't help you unless you have a modulating/condensing boiler. I would encourage you to get a boiler with these capabilities, this would give you a much more even distribution of heat. I think this would get you further down the road than the heat pump idea at this point. Add an outdoor reset, and you won't be needing to use nearly as much fuel to maintain air temps in the building. Why keep your pipes at 170 all the time, and be shutting off and on the water valves all the time, when you can use just one pump, and simply run lower temps in your water to keep the building warm? Let it just idle there, and you will find a much more even heat, rather than super hot, then getting cold, then hot, then cold. The fuel you are burning is astonishing. How many square feet of this building are you actually living in?

I would recommend long before any heatpump thinking, to really insulate and seal, then get a modulating/condensing boiler with an outdoor reset.

pexsupply.com sells them. I installed a nice slantfin bobcat in my home, it is 120,000btu, and it is both keeping my house more comfortable, and using about half as much fuel as my 150,000btu Trianco heatmaker did.

This model is 95% efficiency rating. they make a 200,000btu one too, and they sell for around $3k

After that, you could look into a heatpump setup to make it even cheaper. I think you will have no trouble using only the heatpump for fall, spring and maybe half the winter days. But, you will need the boiler for the really cold ones. In the meantime, you can save up by not spending as much fuel, and work on the heatpump in not as much of a hurry.

Good luck!

[mbopo]

I am guessing your boiler is different - this one is early nineties vintage I think - I wish I could figure out how to paste part of the manual here but here goes the quote I was referring to:
"Inlet temps below 140 deg F can excessively cool the products of combustion resulting in condensation on the heat exchanger and in the flue. Condensation can cause operational problems, bad combustion, sooting, flue gas spillage and reduced service life of the vent system and related components. The bypass...should prevent the products of combustion from condensing in most installations."
I don't have any intention of dragging this all out into a nitpicking argument, as I am guessing you are following the directions for your boiler, and more modern boilers with modulating systems are probably designed to run at lower inlet temps, but unless I get different advice from the manufacturer, I won't be dropping mine below about 160. I did all the installation myself, but I had the local boiler company check everything out for safety and operation and the guy told me to leave my setpoints at 160 and 180. I only repeated that part of the manual here just in case you were possibly doing your system some harm, but it sounds like you are more than knowledgeable enough with your own system, so I apologize if it sounds like I am harping on this point too much. Just didn't want anyone to think I had pulled the 140 deg inlet thing out of an orifice.
i have taken your other advice to heart and am now regretting all the man-hours I put into the installation (1 1/4 threaded pipe manifolds are a bear to deal with) when I should have sprung for a more modern more efficient boiler. The unit I installed was only $500 (used, obviously) and works well and we were not in a position to afford the $8-10,000 we were being quoted for a suitable sized unit - the one you spoke of would have been almost affordable for us and I am sure many percentage points more efficient. Our decision was based on a tight budget, an approaching winter and an ancient existing boiler that was about 78% efficient and actually dangerous (no safety cct on the standing pilot).
Yes we do need to start with making the best of what we have, sealing up the house as best we can and sectionalizing it more and going from there.

In the meantime I have figured out one way to possibly tie a GSHP into our fintubes - keep the systems completely separate and have changeover valves to allow either the boiler or the GSHP system to run water through the heating water ccts. This could be automatically operated using temperature feedback on the piping systems - I am not beyond engineering this myself (PLC's and relay control are my thing), but it would rely on using the same media in both, basically plain water, as there would be some mixing involved during changeover. Anyone out there see any big holes in this idea?

[Christian Nelson]

Key wording in that manual "inlet tempurature". This is assuming that the heat exchanger is running much hotter. From that information, it is pretty clear you do not have a modulating valve. Those are on or off, no in between, this is why they want to keep the difference in temps from inlet to output close.

Newer boilers condense on purpose, you actually have a drain in the combustion chamber to let the condensate out.

I have been down this road trying to fit a boiler in a budget, and bought a used one too. I found that choice to be abig mistake, and ended up much like you for a year, spending way too much on heating costs. This newer boiler I put in, if it continues on the path it is currently on, will pay for itself in less than 2 years from less fuel usage.

Think about it this way, if you only could turn your car on with the gas pedal to the floor, and simply used the brakes and clutch to change speed, no accelerator pedal at all. You would get HORRID gas mileage wouldn't you? That's what non modulating valve boilers do. Another point that is important, efficiency rating is not vey useful on a non modulating boiler, since all that measures is parts per million on your burnt fuel, not how much heat is delivered to your home divided by how much fuel is used to accomplish that task.

So, yes, I agree, with your current boiler you cannot run it at the lower temps, you will simply be short cycling it. However, if you shut the boiler off unless you need it for the colder days, the combustion chamber is not going to be harmed, I assure you. They are simply not wanting the combustion chamber to be heating the water to 180, and having super cold water coming back into it. The expansion/contraction alone would damage it severely!

EDIT: What I am saying is, the heatpump temps at around 140, if the boiler is off will not harm it in any way. This would allow you to run the heat pump unless it's really cold out.

I still recommend upgrading to a modulating boiler first.

[AC_Hacker]

Hello mbopo,

Yeah, I got the email alerting me that you'd posted on the Homemade Heat Pump thread, and I followed the link on the thread and found no post, no explanation, no clue. It was only because of your additional notification that I found this thread. Makes me wonder if other posts have gone missing...

Originally Posted by mbopo

I tried to post a query in your GSHP thread as i can see you have big knowledge in that area, but the moderators moved it to the renovation projects blog and titled it "how to heat a school house". Just wondering if you might get a chance to read it. I do agree with the posts there about insulation but was after some specific ideas on utilizing my existing boiler and fin-tube heaters.
Thanks,Mark

Built in 1957, huh? That was back in the days when petroleum would last forever and ever! My how times have changed.

I'd have to go along with what was previously written, regarding the primary importance of insulation.

There is a very interesting post over at Build It Solar about a couple who also bought an old school house and did the Full Monte insulate-retrofit-upgrade to it. Check it out before you go much further:

Residential Renovation of a Schoolhouse
A Deep Energy Retrofit

This is a very ambitious project carried through to completion. Very well documented, measured and modeled.

One thing that you have going for you is all that concrete, AKA: thermal mass. I think you ought to consider insulating on the OUTSIDE of your concrete walls. This will allow your many tons of concrete to work for you and not against you.

Here's a link to concrete wall insulation.


One thing that you have going against you is all that concrete. It is a conveyor of thermal energy. If you read the schoolhouse retrofit above, you'll see that even after all their amazing work, they are still losing 35% through the slab floor. That's disappointingly high.

You'll also probably have concrete conduction losses through the walls, to other connecting walls, and also down the living-space walls and into the foundation, which is probably not insulated.

Here is some information on reducing foundation losses by building an "underground Styrofoam Tutu" around the foundation (true story).

Christian Nelson expresses his disappointment with fiberglass insulation, and I agree, as evidenced by the fact that I am tearing my home apart and layering six inches of rigid Styrofoam into the expanded wall cavities, and sealing each piece in each layer as I go. It's a huge amount of work, but I can tell the difference it is making. In my case there was no insulation and leaks everywhere. By layering and sealing as I go, I'm adding a high R insulation and completely stopping the leaks. Like I said, it's a huge amount of work.

I still think if it's done correctly, fiberglass can work, but the cavity that contains the fiberglass needs to be completely sealed, all surfaces, all edges, all around. Almost no one ever does that.

* * * * * *

So, to cut to the chase, if you are trying to utilize the existing radiators, you'll need to use a fired boiler (wood or oil or gas). The reason being that a heat pump produces low quality heat (AKA: low temperature). A fired system produces high quality heat and can use radiator units that are smaller than those required for GSHP. If you built a GSHP and used the old radiators, you'd be disappointed, and cold.

As was previously suggested, you ought to consider a modulated, conedensing boiler. The modulated part means that it can vary its output in smooth gradations as heat demand varies. This is more efficient. The condensing part means that it is extracting heat from the water vapor in the flu gasses. this is also more efficient. The efficiencies combine. These units are the state of the art, and are in high demand, and tend to be expensive. But relentless shopping can help.

I'd suggest spending some substantial time studying Passive House practices. And also Superinsulation. These are two similar approaches to robust insulation. It takes a while to see how very thorough these approaches are.

We're entering a new age.

Best Regards,

-AC_Hacker

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[Daox]

Originally Posted by AC_Hacker

Hello mbopo,

Yeah, I got the email alerting me that you'd posted on the Homemade Heat Pump thread, and I followed the link on the thread and found no post, no explanation, no clue. It was only because of your additional notification that I found this thread. Makes me wonder if other posts have gone missing...

Sorry, that would be my fault. I moved the post to a new thread to keep the board clean. I should have left a redirect for a few days.