The Homemade Heat Pump Manifesto

[Mikesolar]

Originally Posted by 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

It's hard to know if the heat load is right. We would have to know all the insulation levels, window type and sizes etc. That said, 4kw heating seems a bit small for a house of that size. I was thinking more along the lines of 12kw and you would be hard pressed to find a 4-5kw oil boiler anyway.

We have fin tube "convectors" which is just a 3/4" copper tube with 3" square aluminum fins on them which could be anywhere from 2' to 10' long. They usually are designed to run at a minimum of 60C and up to 90C, so not very efficient. Along with cast iron rads they were often used with oil boilers. I don't remember ever seeing this type of convector anywhere in Europe during my travels. Your panel rads are way more efficient than the convectors and equal to or slightly more efficient than the cast iron rads but the big definer is how many m2 of radiator surface area for a given room which is why floor heating is such a good low temp system.

[AC_Hacker]

Originally Posted by Mikesolar

...how many m2 of radiator surface area for a given room which is why floor heating is such a good low temp system.

Exactly so! Especially if they are designed with Low Temp heating in mind.

But not all m2's of radiant floor are created equal.

Here is a thermal image of two different under floor installations (which I am not so fond of). The left side of the image shows a floor with spreader plates, the right side shows a floor with no spreader plate.

The heat per m2 is an average of the heat coming off the floor. If the spacing is wide, or if the conductivity of the floor is low (for instance, no spreaders) the heat output will be highly varied across the floor surface, so the feed temp will need to go higher to give the required BTUs per m2. The higher feed temp will affect a fossil fuel burner to some degree, but it will affect a heat pump to a much higher degree by reducing it's efficiency.

-AC

[Mikesolar]

My favorite way to do underfloor heating is with a gypsum cement (screed in the UK) then some engineered wood, tile or linoleum over top. If there is no other way then attacking it from below is OK but the extra wood is higher insulation value.

Jim, how thick is the wood over the heat plates?

[AC_Hacker]

Originally Posted by Mikesolar

My favorite way to do underfloor heating...

I should have said that under subfloor is not my favorite. A wet system like you are describing is a whole different story.

-AC

[Northern Diver]

Originally Posted by Mikesolar

Jim, how thick is the wood over the heat plates?

We have 3/4" tongue and grove floorboards with 8-10mm laminate floor laid over the top, so probably just a little over 1" in total. There are a couple of problems with doing a wet fit from above:-

• The traditional floorboards were laid prior to interior partition walls so extend underneath. No simple way to lift them without demolishing the whole of the downstairs interior.
• The main living space is now made up 50:50 of old and new, with a continuos floor running between them. changing the flooring level is not an option.

My thinking at the moment is along the lines of doing the under floor works first, using substantial spreader plates and as much insulation as I can fit between the joists, making sure everything is air tight down below. If the floor radiates enough heat (at a low water temp input) then I can think about doing the heat pump.

I'm really not worried about the radiators, there is plenty of scope for fitting larger units, or space is more limited, upgrading to double panels. and seriously, the areas covered with radiators rarely have them turned up at the moment.

[Northern Diver]

Originally Posted by Mikesolar

It's hard to know if the heat load is right. We would have to know all the insulation levels, window type and sizes etc. That said, 4kw heating seems a bit small for a house of that size. I was thinking more along the lines of 12kw and you would be hard pressed to find a 4-5kw oil boiler anyway.

Here's how I worked out my current heat load.
Since 22/8/2007 I have purchased 21,115 ltrs of domestic heating oil.
that's 10.122 ltr per day.

1 gal of domestic heating oil produces 138,500 BTU per US Gal
Converting my 10.122 ltr per day to US Gallons gives 2.67
which is therefore 401092 BTU per day
or 16712 BTU per hour.
My boiler is listed as having 85% efficiency so actual heat output is
14,205 BTU per hour.

Do those calculations make sense or am I missing something?

Regards
Jim

[Mikesolar]

Hmmm, not really. Your math doesn't account for variations in outdoor temps and indoor temp, number of running hours in a year, DHW vs space heat (assuming oil is doing both), solar gain, wind losses on walls.

The simplest way (but least accurate) is to look a the walls, roof, floor and find, on the web, local buildings with he same construction make an educated guess compared to those buildings. Not great but it will be closer than what you have done already.

I can say that in shetland the low temp is around-1C and is rarely below that so perhaps we are looking at half the heat load of Toronto. Most reasonable insulated houses here have a load of about 30-40w/m2 so perhaps you would be 25w/m2 or so....at design temp so you would have to supply 3kw (very low). It is within the realm of an ASHP. The GSHP in my mind is a waste of material and time.

[AC_Hacker]

Originally Posted by Mikesolar

Hmmm, not really. Your math doesn't account for variations in outdoor temps and indoor temp, number of running hours... The GSHP in my mind is a waste of material and time.

This thread is beginning to look like a radiant floor thread with a possible option for Heat Pump later on.

Regarding the purpose of this thread (The Homemade Heat Pump Manifesto), namely how to create a working heat pump from some other source, with DIY ground source heating being the ultimate aim, these posts are way off topic.

Marksolar and Northern Driver, there is no other place on the Internet which invites and encourages experimenters to work with heat pump conversion, and also to DIY their own ground source loop field. This thread is very precious real estate, and you are occupying this space with off-topic posts.

Mikesolar, your opinion about GSHP is just that, your opinion. If you would like to discuss this more fully on another thread, I would welcome that.

Northern Driver, since you have not actually made up your mind to use a heat pump at all, you are taking up space that would be better used by people who have made such a decision and are seeking information on how to actually proceed.

If either or both of you start another thread, or append this conversation to the DIY Radiant Heating for instance, and contact Daox, he can easily move your posts to that new thread.

Thank you for your cooperation...

Sincerely,

-AC_Hacker

[Northern Diver]

AC,
You are of course correct. There are other threads in this forum that suit these recent posts better. My original post was about the suitability of a compressor I found on ebay "Samsung R22 Rotary air conditioning refrigeration cooling compressor 48A124JV1EG". Samsung R22 Rotary air conditioning refrigeration cooling compressor 48A124JV1EG | eBay
By combining your post about the degree days with my latest calculations converting oil consumption to BTU, then it would seem like this unit with its peak output arroud 24000 btu/h is not hugely over rated for my needs. and with our current rate of electricity charges even if run continuously would still cost less than the oil.

[Mikesolar]

AC, I am all for GSHP's and experimenting with them. I only wanted to point out that the conditions that make GS suitable also apply to ASHPs, in this case.

Of course, there should have been a new thread about this install. I don't know about that particular compressor and whether you can get replacements if need be. I would be looking for a Danfoss or Copeland if possible but that is just my opinion.