The Homemade Heat Pump Manifesto

[SDMCF]

Originally Posted by AC_Hacker

A GSHP is pretty much the most economical form of heating you can have. But it is not like running you are going to run GSHP right into your ordinary house heating system and expecting everything to work just like it did before, only cheaper.

and

You can't use the methods that worked for heating with wood, coal, gas, oil, etc. because these methods produce much hotter temperatures than a GSHP is capable of... things need to be done in a different way.

That's a reasonable rule of thumb but as always "it depends". I just installed a GSHP and connected it into my existing heating system (radiators). I didn't change anything inside the house apart from connecting the GSHP into the central heating pipework. Everything works just like it did before, only cheaper.

One of the most important things to bear in mind is that a GSHP will produce hot water at a temperature of 120F max.

That is indeed the crux of the issue, although I would say 55C/130F. My GSHP manual claims 65C/159F but I don't believe that. My radiators run at a maximum of 55C so I just about cope during really cold spells, but of course usually it is not so cold and the radiators don't need to be so hot.

There are three big things that can lower the required water temperature:

1. Minimize the heat loss in your heated space by reducing the infiltration (air leakage) to the very minimum.
2. Increase the quality and quantity of insulation significantly above the required code level.
3. Insure that your heat input method, forced-air or water heated radiating panels, are as efficient as possible.

Maybe a 4th option is to install more radiators (or whatever you use).

[SDMCF]

Originally Posted by DonT

A friend has a mini-excavator I can rent for $100, so I can trenching in a ground loop about 8 to 10 feet deep.

Is that normal in your area? It seems very deep to me. Folks in my area seem to think it is counter-productive to go too deep. I believe the thinking is that the ground temperature lower down won't "recharge" so well during the summer. Around here 1.5 to 2m is common.

[AC_Hacker]

Originally Posted by SDMCF

That's a reasonable rule of thumb but as always "it depends". I just installed a GSHP and connected it into my existing heating system (radiators). I didn't change anything inside the house apart from connecting the GSHP into the central heating pipework. Everything works just like it did before, only cheaper.

I think you need to give some details regarding your radiators. The reason I say this is that North American radiators are typically about 50 to 70 years behind the technology that is normal in your area.

Additionally, by going to more efficient radiators, which will lower the feed-temperature, the increase in COP is exponential. It is a mild exponential curve, but exponential nonetheless.

-AC

[SDMCF]

Originally Posted by AC_Hacker

I think you need to give some details regarding your radiators. The reason I say this is that North American radiators are typically about 50 to 70 years behind the technology that is normal in your area.

I nearly spat out my coffee! That did make me laugh.
You may be correct that more modern technology is normal here compared to North America, but if you saw my house you would understand why that idea is comical in my case. I have 2 types of radiators.

I have a few radiators something like this:
http://thumb9.shutterstock.com/displ...-288271046.jpg
My guess is they were old, re-used units when they were installed.

Most of the radiators radiators are slightly more modern, something like this:
https://images.duckduckgo.com/iu/?u=...ater01.jpg&f=1

I believe all the radiators were installed in the 1960s.

[AC_Hacker]

Originally Posted by SDMCF

I nearly spat out my coffee! That did make me laugh.
You may be correct that more modern technology is normal here compared to North America, but if you saw my house you would understand why that idea is comical in my case. I have 2 types of radiators.

I have a few radiators something like this:
http://thumb9.shutterstock.com/displ...-288271046.jpg
My guess is they were old, re-used units when they were installed.

Most of the radiators radiators are slightly more modern, something like this:
https://images.duckduckgo.com/iu/?u=...ater01.jpg&f=1

I believe all the radiators were installed in the 1960s.

SDMCF,

Very sorry to hear about your ruined coffee by spitting in it. Did you drink it anyway?

The top heater can still be found. It was originally meant for steam heat, and as it was designed, steam condensed in it and the radiator gave off considerable heat. Just running hot water through it would yield far less heat.

The bottom heater is now being sold in the US as a high-tech premium heat radiator. Not many people have them.

There is another radiator that is between the two you showed.

These are everywhere here in the US, and many people here don't know of any other kind. These things work well, but they are designed for water temps around 150F to 180F. And yes, if you get enough of them it would be possible to heat a house.

But I came across some radiators that are specifically designed for low feed temps. Here is an image:

In this case, they have very large fin area, and the small computer type fans gently keep the air moving. This pic is from a product made by Jaga. It that a Finland firm?

My point is that yes, if your phase change system is running at 120F it will work and will be cheaper, but if you can use a more efficient radiating system, you can use radiators that give you the heat output you need and use lower temp water, and you will be even better off.

-AC

[DonT]

Originally Posted by SDMCF

Is that normal in your area? It seems very deep to me. Folks in my area seem to think it is counter-productive to go too deep. I believe the thinking is that the ground temperature lower down won't "recharge" so well during the summer. Around here 1.5 to 2m is common.

the frost line as required by MN state is 42 inches. last year we a lot of frozen waterlines that are down about 5 to 6 feet, so I think deeper is better

[DonT]

Out of curiosity, did you insulate your 12ft x 18ft slab and it's edges from the ground with about 2 inches of high density blue or pink insulation board?

I have 2in high density GREEN (lol) on the floor and I went up the sidewall and around the post. the slab is about 4in thick so I went up about 6in

[DonT]

Some questions for you:
Where is it that you live? what's the nearest town?
How much do you pay for a kW-h of electricity where you live?
What is your ZIP CODE?
Your $4.96 per day was only for the electricity to the heater only and not to anything else like lighting or anything?
did you have a circulation pump going all the time?

as I said I live on the Iowa-Minn state line near Northwood,Ia
the local utility company as a load program where they can shut you at high peak loads, in return kw's cost $ .064 instead of $ .105. so I pay $ .064

zip code 50459

For the month of January it cost me $4.95 per day for my heat and hot water (potable). this was not very clear. all that the $4.95 is for my hot water heater(boiler) for the floor and the hot water heater potable (drinking )

no the circulation pump on runs when I need heat, if it ran all the time I think I could set the water temp to about 100 to 120. problem is how to adjust it as temp changes

[DonT]

But the most important thing you need to know is how much heat does your house require in the worst months? In other words, how much is it losing?

I can calculate it for you if you tell me your price per kW-h, and zip code.

thank you
I did a heat loss calculator online. At a design outdoor temp of -20 and 0. I tried to be conservative with the R-values and it has design loss of 17483 and 13598

it would be nice to know if I'm any where near right

[DonT]

I took the kw's I used for Jan, 2400 kw's and converted it to btu's per hr.
2400 * 3412.142 = 8489140.80 / by days / by hours = 11006.91 btu/hr for the month