The Homemade Heat Pump Manifesto

[Northern Diver]

Hello all, I've been reading the thread through for a few days now and am really inspired to get going with my own project.

Living in Shetland, used AC units aren't exactly easy to find, but I did see this:- /itm/Samsung-R22-Rotary-air-conditioning-refrigeration-cooling-compressor-48A124JV1EG-/221220173009?pt=LH_DefaultDomain_3&hash=item3381bf f4d1 - Samsung compressor on Ebay which would seem to fit the bill as somewhere to start. ( I can't post links as I am new to the forum)

We have plenty of land to put trenched ground loops in, being tenant farmers, we have 3.14 hectars (7.7 acres) or 107,000 sq ft. right next to the house. The only problem I can see is that getting the trenches very deep could be an issue as there is not a great deal of soil, probably 4-6ft before bedrock.

I'm off to look at our oil heating bills and try to work out what heat consumption we have been running at, I think it's way higher than this unit could produce, but we have some radiant floors which we could put on to heat pump and keep the oil boiler for the radiators, or even use multiple Heat pumps to get the capacity need in the winter, only running one in the summer for hot water.

Cheers
Jim

[Mikesolar]

Your best bet is to get the running temps of the rads down to that of the floors. If that means putting more rads in , so be it. From my heating engineer friends in the UK, I am told that the most trouble is with high temp heat pumps so sticking with lower temp ones (40C) is going to be an advantage in terms of reliability.

I am speaking in terms of air source HPs but the same holds true for ground source as well.

[Northern Diver]

Mikesolar,
Downstairs there is scope for retro fitting radiant floor heating in the areas currently covered by radiators. These areas are in the original portion of the building, the floors are suspended wooden floors over a couple of feet air gap then bare soil, access from underneath is uncomfortable but entirely possible. Fitting the insulation that would go with the radiant floor system would, I think, already make a big difference to keeping the building air tight. Upstairs we don't need quite so much heat, and fitting larger radiators is certainly possible though the rads currently fitted don't run anywhere near their full capacity. The new portion of the house is very air tight and well insulated, the wall construction is Beco Wallform, a kind of polystyrene lego with fiber reinforced concrete core. So I think sticking with lower temp should be OK. I can always keep the existing boiler in the system for the days that the heat pumps can't produce enough.

[AC_Hacker]

Originally Posted by Northern Diver

Hello all, I've been reading the thread through for a few days now and am really inspired to get going with my own project...

Welcome to the conversation, Jim.

In your milder climate, 4 to 6 foot deep trenches can work, but you you'll surely need more of them.

There's an interesting crew of people here, with a wide and deep range of experience, willing to help you out. The more information you can give us about your project (goals, measurements, photos, updates, etc.), the better advice we will be able to share with you.

One place to start would be if you can tell us the degree days of your location. There is a website located HERE that can provide this for you. If you can give us this info, in both Celsius and Fahrenheit it will be best. By the way, you can't just calculate the degree days in Celsius and then convert that number to Fahrenheit... it doesn't work, you'll have to run the calculator twice, once in each system of measurement. If you need help with this part, just ask.

Then details about your house: size, insulation, etc.

It's going to be an adventure!

Best,

-AC

[AC_Hacker]

Originally Posted by Northern Diver

...and fitting larger radiators is certainly possible though the rads currently fitted don't run anywhere near their full capacity...

Jim,

One of the things you're going to run into is that oil heat is very energy dense... in other words the oil-fired boiler will put out relatively high temperature water. If you go with GSHP, your compressor will not be able to deliver water that is as high in temperature as you had before.

So you will be working with Low Temperature Heating. Much of the lore concerning heating assumed high temperatures. Most oil heat radiators are designed to deliver the required amount of heat from high temp water (around 71 C). Your GSHP will struggle to deliver water that is 49 C, and it will be more efficient if it doesn't have to raise the temp that high.

So, one fix is to do as Mikesolar suggests and get more radiators. Another approach is to get radiators that are especially designed for Low Temperature Heating. The exist, they're expensive, but you might be able to make your own.

This same thinking goes for radiant floors... and even more so.

The general concept is that low temperature heating requires more area to radiate.

And as you go along, anything you can do to reduce the loss of heat will be to your benefit, no matter what kind of heating system you go with.

-AC

[Northern Diver]

AC,
The degree days in Farenheit 5-year average and a base temperature of 65F are below.
HDD % Estimated
Jan 778 11
Feb 710 6
Mar 708 7
Apr 603 6
May 518 7
Jun 401 8
Jul 301 8
Aug 291 8
Sep 366 6
Oct 546 8
Nov 627 8
Dec 814 8
Total 6663 8

I've worked out my oil consumption averaged over 8/2007 to date and have come up with 10.12 ltr (3.8 gal) per day. Assuming 135,000 BTU for Kerosene that works out at 11,278BTU per hour (75% efficient, non condensing boiler)

As for construction, size etc, the house is on two stories, 970sq ft upstairs and 1300 down stairs. Construction split between the older front portion of the house, 1370 sq ft which is mass concrete, walls approx 18" thick with air gap of a couple of inches then 4" fiber glass insulation before the surface finish of plasterboard.
The rear of the house, 900 sq ft is constructed of 313mm Beco wallform blocks with a polymer render on the outside and fiber reinforced concrete core and plasterboard finish on the inside. (5.44msqK/W). The roof over the older part of the house is traditional slate over close boarded timber and 4" of fiberglass insulation. The roof on the new part of the house is Jablite Slimfix SIP with Decra outer covering, all sitting on three parabelum composit beams, for a U value of 0.2.

Just writing this description and looking through all the documentation generated from when we had the addition built, I can see that as well as fitting radient floor heating to the front portion downstairs, the insulation in the old roof and the older exterior walls certainly has some scope for improvement.

Jim

[Mikesolar]

Originally Posted by AC_Hacker

Jim,



So, one fix is to do as Mikesolar suggests and get more radiators. Another approach is to get radiators that are especially designed for Low Temperature Heating. The exist, they're expensive, but you might be able to make your own.



-AC

AC, the low temp rads (Stelrad, Centre rad, Myson) are standard in the UK and the prices are 30% of what we buy the same one for here. The market in Europe is way bigger

[AC_Hacker]

Originally Posted by Mikesolar

AC, the low temp rads (Stelrad, Centre rad, Myson) are standard in the UK and the prices are 30% of what we buy the same one for here. The market in Europe is way bigger

It sounds like Jim is doing an upgrade from oil-fired to GSHP, are you confidant that his existing hardware is low temp? Do we know how old his existing hardware is?

-AC

[Northern Diver]

AC,
The radiant floor heating is only 5 years old, and actually works on a lower temperature than the boiler outputs, there is a thermostatic mixer valve which mixes the boiler produced hot water with a portion of the return from the under floor coils. One of my first tasks is to identify what the temperature of the water that feeds in to the floor circuits and to assess how well they will operate at achievable temperatures.

The radiators are a mix of high output stelrad units, but if I go ahead with this I will be changing the whole of the downstairs to radiant floors. I can access all the floor area that is not already radiant from underneath and have been meaning to insulate under there for some time, so it seems to make sense to fit piping and spreader plates at the same time.

The cost of replacing the four radiators up the stairs with higher output units is not out of the question, but I really believe only one would need replacing, the other three are rarely turned on, and if they are on they are set very low.

what is really worrying me at this stage is my calculations for the thermal input I currently have. I have calculated an average heat input between 11,000 btu/h and 14,000 btu/h depending on the sources I have used for the energy density of heating oil and the efficiency of the boiler. Does that seem reasonable for a house of this size with these degree days?

Jim

[AC_Hacker]

From the data you gave us:

HDD Yearly Chart




HDD Yearly Data

Does this seem correct to you?

The monthly hourly BTU rate is on the average, and your design should go somewhat beyond that to account for the lower temperature swings.

-AC