Heat pump connection to radiant floor
 

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

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

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

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

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.

Etech Heat Pump...
 

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

E-Tech, etc.
 

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.

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

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

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

Myself! We have the land area here, and I'm building a small (1200 SF) house on the lot across the lane from us, so I want to put a system in both places. I will hire help from time to time, but I want to be responsible for the work and workmanship. Besides, I enjoy working; I don't enjoy watching. We'll see what kind of song I sing after I've dug a kilometer's worth of trenches.

If you search E-Tech W102 heat pump, the top hit just now was "www.etechbyaosmith.com/com_waterheating.html". The page is new, but the product may be on the verge of a revival. I have the catalog and owner's manual for the heat pump. It's odd that one or two don't show up on eBay or somewhere.

I have some questions and thoughts about source loops, so I'll be back on this or other threads. Besides, I've got days and days of reading ahead...mm

Ahhh! Remember, that was a 1984 price!

Michael

Good going. You will see some of my posts on the manifesto. We as well had the oil thirsty hot water heaters suppling or home for heat. The hot water was circulated in our concrete floor via 5/8 dia Kitec, Nice stuff but like the poly B you have, it has been discontinued.

The system worked extremly well but the price of oil OUCH. We have installed solar hot water with Geo-thermal back-up and it has me and my family grinning ear to ear. We are in Canada and it can get a little cold but the geo-thermal just hums away. It operates sometimes continuously and in fact losses a little ground when the outside temps drop harshly. This is the 3% that AC-Hacker is talking about.

Your in-floor Poly B sounds perfect it will perform well at the lower supply temp. 85-110 Deg F.

For our area here the rule of thumb for the ground loop is 600 ft for each ton of heat-pump. Your milage may very. The nice thing is if you over install too much ground loop its a good thing. Higher efficiency.

We even went so far as to install our own homemade Geo-thermal heat pump in my shop. I installed 4 tons of loop and started with a 2T pump. Its working OK and saving some serious cash. The shop temp is between 14-18 deg C running full out. Fine for the shop.

Your install can be amazing. I'm on the edge of my seat imagine, a heat-pump powered with a 5.5 Kwh solar array. Thats holy grail stuff. My 2T unit is only 1500 watts 1.5 Kwh.
6 hrs of run time as the sun is powering the array warming your concrete floor. WOW

Randen

Hello randen, When you write "the ground loop is 600 ft for each ton," what sort of 600 ft do you mean? What width of trench, and what configuration of pipe in the trench? Straight pipe side by side or separated by the width of the trench or above and below? Half, third or quarter pitch slinky if slinky at all. Is the 600 ft the length of the trench or the length of the pipe in the trench. I'm thinking of the bore hole style where you may have a 200 ft deep hole, but you'll end up with 400 ft of pipe. A half pitch slinky in a 3 ft wide trench might take 12-13 ft of pipe to travers 18 inches of trench including the return pipe. The number of ways the source pipe can be installed is a little challenging.

The first thing I would say is that the tubing spacing should allow you to run 85F-90F water and still heat the place well. You cannot have a high worst case deltaT to over come like in the north. This will only have to raise the temp 30F-40F worst case.

Michael

I don't proffess to be an expert on the subject but a bore hole can be expensive if you don't have the room and I'm not sure of the ratio of piping because you may enter the water table somewhere in your depth and this may reduce the amount of piping (depth)required.
For our installation in my area I did ask around. A reliable installation for a trench here is 6 ft below ground in a 4 ft wide trench two loops not getting any closer than 2 ft apart each tube. The tubing was 3/4" HDPE designed for that application and welded connections. The installers had cautioned about the slinky installations, although the amount of tubing that goes into the trench gets used up the fact that for many feet of tubing are essentually overlapping and its not as good as having a minimum of 16" of dedicated zone of earth for heat collection. Now again this may be a specific detail for our harsh climate. We are subject to some wind swept areas that the ground will freeze down to 4 ft below grade. You may be able to source enough heat 1 ft below grade because your milder climate has injected enough heat into it.

I would check around locally. its a lot of time and money to not have your loop installed correctly.

Randen

Good information. Thanks. I only mentioned a bore hole as an example. It's not what I intend to do. The amount of red tape in this county for a drilling permit is prohibitive for me. It's a very water sensitive area, and the burden of proof that I wasn't drilling wells would be too great, so that approach is not being considered. I took a years worth of temperature samples at the surface, 20", 40" and 60" down in the area where the source pipes will go. I put four sensors in a piece of 3/4" pvc pipe, capped the lower end, filled it with dry sand to keep the sensors in place and give conductivity, put a u-bend on the top to keep water out, and recorded the temperatures every night for a year. The upper sensor varied between 48 and 73. We're close to the Pacific which is a great stabilizer of the local temperature. The lower sensor varied between 55 and 64. The sensor at 40" below the surface varied between 52 and 65. It seems to me that 48" deep wd be just fine for the source pipes. I'm imagining I can dig a narrow slot type trench four or more feet deep and bury the loop with the return portion in the bottom and the out going portion of the loop perhaps 2.5' down with each loop being about 300' long in a 150' trench. At 2' apart, I have room to install ten loops for a total of 3000' of collector pipe for a 2.5 ton heat pump. Perhaps that's far more ground source pipe than I need, but in order to find out, I'm installing one such loop which I'll connect to my small E-Tech heat pump, and monitor the rate at which I can extract heat. It should give me sufficient data in order to design the heat exchanger we need. mm

GSHP Fever...
 

Hmmmmmm......

"You might be an ecorenavator if you take a year's worth of readings of ground temps before you start digging."

This info is solid gold.

Can you put this data online or in graphical form?

This is the kind of thing everybody ought to do if they're considering a GSHP.

You clearly have GSHP Fever, and there's only one cure...

Best,

-AC

A question for AC: I have many related questions and topics I'd like to discuss, but would it be better for me to switch from this thread to the Manifesto thread to keep all the relevant stuff in one place? You know your way around this forum, and I'm an absolute newbie, so I could use a little guidance. Also, this thread has morphed from one about my little heat pump being directly connect to a radiant floor system to one about heat source design. I don't mind moving through lots of topics, but I don't want to run against the practices of this forum.

And, I'll work on getting the ground temp data in some sort of graph or chart. Right now it's in pencil on a ledger sheet along with air temp outdoors, in my attic, and water heater run time on a daily basis. mm

Michael does the E-tech HP xfr heat from input water to output water within the unit or does it require buffer tanks on the side from which to exchange?

Hello Drake, It is totally self contained. It has a circulating motor in the box that runs the source water, and a flow switch senses when the hot side has water moving in it which powers up the circulator. Cold potable water goes in, and hot water comes out, and that hot water can, of course, go into a holding tank to build up a reserve of DHW.

mm

Good call.

Yes, the aspects that deal with the heat pump itself and the loop field would be a very good fit for the Manifesto.

The radiant floor aspects, though very closely related would be better put in a thread pertaining to radiant floors. There are two or three radiant floor project threads. You might look them over and decide if you'd like to be part of them or start your own thread.

Where ever you end up posting your floor info & queries, it might not be a bad idea to link them to your Manifesto posts, and also link from there to your floor posts.

We should have encouraged this kind of cross-linking a long time ago.

Good luck!

-AC

Any chance you'd pass along some clues as to how to do this?

Sure...

Finding the thread that you yhink is appropriate, I'll leave up to you.

Every thread has a beginning and a last post.

And every post in the thread has a 'permalink' URL in the upper right corner.

I think that the easiest way to do this is to open two windows, one is the FROM window, and the other is the TO window.

So, in the FROM window, in the body of your post, you might have some text that you want to use make a hyperlink with... your text might be something something like LINK TO THIS POST.

Then in in the TO page, go to the permaling, and right-click and choose 'copy link address' or whatever is the equivalent option for your browser. Choosing this will buffer the URL of the page you want to link to.

Then you go to the FROM page and click+drag your mouse over the text like LINK TO THIS POST. Once it is highlighted, look at the tool bar above it and you will see the hyperlink creating button (it looks like a globe with a chain in front)... click that button, and a box appears that invites you to put in your URL. At this point, you right-click your mouse and choose "paste'.

That's it. It's easier to do than to explain.

Best,

-AC