Heat pump connection to radiant floor

[michael]

I have an older Etech water to water heat pump rated at 1 ton/12000 Btu, and we currently heat using a 30 gal Bock oil fired heater connected via a heat exchanger to a radiant floor (tile over 1.5" concrete over plywood over an insulated crawl space). The system is in its 26th year, self designed and installed including the heat exchanger. I'd like to substitute the heat pump, or perhaps a newer and somewhat larger one for the floor heating function of the Bock heater. Currently the water heater does both DHW and the floor.

Does it seem likely that the heat pump could be connected directly to the floor with the hot water output going directly to the hot floor manifold and the floor return going immediately back to the heat pump. The output temperature from the heat exchanger is about 120 deg modulated down to 110 by means of a tempering valve that injects some of the cooler return water into hot coming from the heat exchanger. The balance of the return water from the floor goes back to the heat exchanger, and that is typically about 78 deg. We keep the house at about 70 deg. all day and night, every day.

I don't understand enough about the nature or workings of a heat pump to know how it will react to return water in the high 70 degree range nor how to control its output to about 115 deg. Is it likely that I'll have to install a tank between the heat pump and the floor to act as a buffer with circulating pumps on both sides of the tank? Does anyone have a situation like this that can provide some suggestions. Is an appropriately sized heat pump a viable alternative in this case as we have sufficient ground area for a reasonably sized array of heat source pipes.

Michael Moreland
Mendocino, CA

[AC_Hacker]

Originally Posted by michael

...Is an appropriately sized heat pump a viable alternative in this case as we have sufficient ground area for a reasonably sized array of heat source pipes...

Well, Mendicino, huh? ...so you won't need so much heat as compared to Wisconsin.

Have you done some kind of a heat load analysis on your place?

Also, when your old boiler was working, did you happen to see what the water temp was going into your floor?

And do you know what the pipe spacing was for your floor?

These are a few of the things you need.

Best,

-AC_Hacker

[michael]

Thanks, AC_Hacker, for your response. You are correct, we don't need any where near the heat our Wisconsin friends do...but aren't you from Portland? I grew up there, and don't remember it being all that harsh! There was a heat load analysis done back when we got the building permit to build this house in '88, but I also know from keeping track of our water heater that the heat load is about 60M Btu per year, and DHW is something a lot smaller tacked on. The water heater...that's really all it is, but oil fired...is still in use. I've just begun messing around with the heat pump. We have 1000 SF of radiant floor. The tubes, arranged in 10-200' loops joined in a manifold, are 6" OC except in the bath where they are 3-4". The water temp going into the floor is steady at 110 deg. There is a heat exchanger between the water heater and the floor system that outputs water at 120-125 degrees, and a tempering valve mixes return water from the floor to cool the water entering the floor loops to 110.

I haven't found anyone on the coast or inland, say in Santa Rosa, that deals in ground source heat pumps, so this website, which I just recently found, seems like a godsend to me. After thinking a while about my first post, I've begun to plan an experiment to see how the Etech heat pump behaves. We have a 5000 gallon water storage tank for domestic use, the water coming from our well. I can use that water as an open source heat supply, and since the water came out of the ground, it's temperature will be a good measure of what pipes in the ground could supply. I can extract about 400k Btu by lowering the temp from 55 to 45 degrees. Then I can watch what happens on the production side of the heat pump, setting up a situation that will mimic what would happen if it were connected to the floor loops, that is, output water at 110-115 degrees, and return water at 80 running continuously for a couple hours. I should be able to get some idea what the heat pump can do.

I'm pretty sure we'll need something bigger than this 1-ton because on the coldest days our house requires about 200k Btu for heat, and that would require running it nearly all day. I'm working on reading your posts...that may be the best textbook I could find. mm

[AC_Hacker]

Originally Posted by michael

I'm pretty sure we'll need something bigger than this 1-ton because on the coldest days our house requires about 200k Btu for heat, and that would require running it nearly all day. I'm working on reading your posts...that may be the best textbook I could find. mm

Well, I was all prepared to tell you you wouldn't be able to do it with GSHP, but your floor layout sounds really great.

I'm going to be away for about a week, and I'll be glad to help you all I can when I get back, but there are some really competent folks here, too.

So, here is the general idea, your house will exhibit some number of BTU's of heat loss on the very coldest day. But then there are what they call the 3% days, where it's not quite so cold. You are better off designing for the 3% day and using supplemental heat for the really cold day (or two). Reason being your heat pump will achieve it's greatest efficiency when it is run full out.

And you will need some amount of loop field that is at least big enough to supply your heat for the 3% days. If your loop field is too big, it's not a bad thing at all, because the seasonal temperature drop will be smaller. But a bigger loop field will be more expensive. Trade-offs.

And then you'd want to choose a heat pump that could move the heat for the 3% days from the field into the house.

But you already have your heat pump, a 1 Ton job.

So what you need to do is a heat load analysis. HERE'S A PRETTY GOOD ONE over at Build it Solar. Be honest when you do this measure carefully. It should give you a pretty good idea how much heat you're gonna need.

The look and see how that matches up with the heat pump you already have.

If your heat load is smaller than what your heat pump can provide, you are 'in high cotton' (a Southern expression meaning thing s are looking good). If you come up short, your choices are:

• Go after all the infiltration leaks you can find
• Inuslate, Insulate, Insulate
• Use the unsufficient heat pump anyway and fill in the rest with your usual heating methods
• Get a bigger heat pump

Personally, I would recommend doing everything you possibly can to prevent your house from losing heat before you start thinking about cheaper ways to get heat.

After a rigorous attack on heat loss, you may find that previously insufficient heating methods have become sufficient.

Another thing you may want to consider is that due to your mild winter, an ASHP might be a good choice for you. Unless you are really handy with heavy equipment, doing a loop field is not a trivial affair.

Also, ask around locally what it takes to do a 1 Ton loop field.

That's it for now, I'll be out of touch for a week...

Enjoy the Manifesto. There's also an excellent thread on DIY radiant flooring that addresses many of the related issues. The two really go together.

Best,

-AC

[Drake]

Micheal could you give more info on where you got a water to water manufactured heat pump that small. I have not been able to find W/W HP that size, only larger.

[AC_Hacker]

Drake,

Unless I miss my guess, he has an Etech air-to-water heat pump that was originally sold as a retrofit for an existing water heater, similar (only bigger) to the A7 units that Xringer and others are getting.

Etech was a division of AOSmith. Although they work well, and as advertised, I think they never took off because they're probably a bit over-sized for the average water heater, they were selling for $1600, and the price of energy was still too low.

I actually had one (still do if I want it back) to use as a ASHP in my hybrid heat pump system.

HERE is an article about the little wonder.

In the instructions, it clearly states that the unit is intended to be used indoors. It is evident that this is so as, the compressor has no sump heater to assure startup in winter, and the overall unit is subject to corrosion when left in outdoor conditions.

I decided that for my purposes, getting the outdoor unit of a 12,000 BTU mini-split unit and modifying it, with the addition of a suitable brazed-plate HX to heat water, would be a better alternative for me.

Although my searching was not able to locate an Etech water-to-water heat pump, if michael's unit actually is one, it could have been user-modified from an ASHP Etech unit with the addition of a water-to-refrigerant evaporator HX.

I noticed that my Etech had a tube-in-tube coiled condenser HX, which would be required for an open system water heater (water heaters are, by default, open system). So his would need two of these, or similar... and no air coils and no big fan.

I'm interested in michael's response, to see how close I actually got to the target .

Best,

-AC

[michael]

Sorry to keep you wondering. Here is what I know: The E-Tech was a gift to me from a friend who, in the '80s, was experimenting with energy saving devices. It's a W102 water-to-water heat pump designed to feed into an indirect fired water heater. I have the original invoice which prices it at $607 on Jan. 26, 1984. I have never used it to heat our water or our house, but the last time I tried it, a couple years ago, it brought five gallons of water up to 125 deg in a few minutes using our 5000 gal storage tank as a heat source at about 60 degrees which is what the specs predict, i.e. 20 gph from 55 deg to 125 with 60 deg source water. Here are a couple photos of it with the shroud on and off. It seems like a very good little unit but quite a few years ahead of its time. I have recently agreed to trade it to a friend who will help me build and program a data logger since it will prove to be too small for either of the situations in which I hope to employ a heat pump.

[michael]

And there's more...the first thing being that the heat pump manifesto thread is one hell of a long thread, and pretty slow going if any of it is going to really get absorbed. I'm not getting anything done while I work my way through all those posts, but it's very interesting. That hardly says it!

I'm on the this message board in hopes of getting ideas for switching our heating systems from oil fired to electric heat pumps. I don't want to build my own, but I do want to install the system, and this seems like the first place I've found where I can get some practical advice for doing it. There are two houses on this property with radiant floors installed. I did the installation of one 25 years ago, and the other about 15. They both use 1/2" polybutylene tubing...it's what was available then. The first one used the manifold provided by the manufacturer, and since it was never pressurized, it lasted until last year when it began to leak, so I built a new manifold (ten loops of about 200' each) using Sharkbite connectors. It's pressurized now to 12 psi, and the system still works well. The newer one has always been pressurized, and they both run off of Bock 30 gal. oil fired water heaters. I built both heat exchangers from 1" and 1/2" copper tubing, so the floor loop water is kept separate from the water in the Bock heater, and they have worked flawlessly since installation.

However, I'd like to get off fuel oil. I began a process of making us less fossil fuel dependent two years ago when I designed and built a 5.5kW solar array. I think I'll put that information on another thread in the appropriate forum, but it got me thinking about how good it would be to stop burning fuel oil. We generate more electricity than we use, so it makes sense to me. I'm not the least bit worried about the mechanical aspect of converting to a heat pump, and I don't mind the thought of purchasing a new, appropriately sized one, but I'm daunted by the ground source heat exchanger. I understand AC's suggestion that we use an ASHP instead, but it will require back up, it's less efficient, and for plenty of other irrational reasons, I am stuck on the idea of ground source. As for now, I'll just keep reading the manifesto. mm

[AC_Hacker]

Originally Posted by michael

... it's a W102 water-to-water heat pump designed to feed into an indirect fired water heater. I have the original invoice which prices it at $607 on Jan. 26, 1984...

Well, it looks real enough. But even knowing the model number, I can't find it on the Internet.

So, it sound like you are on the 'loop field' part of your quest.

Are you going to have it done for you by a company that specializes in that kind of thing, or are you going to do yourself?

-AC

[Drake]

That size/price manufactured W/W heat pump is my Holy Grail.