Domestic Heat Pump System

My parents have had a sanyo CO2 eco system installed.

I was very doubtfull of its effectivness however so far (hot water only) it has been superb)

i am in the process of buying a house that does not have a mains gas supply and currenly has an LPG combi boiler.

As lpg is more expensive im seriously thinking about chnaging the boiler etc.

Im concerned of the noise of the outside of the unit and wondered if an air unit would be best. There is a well at the house and plenty of area for a ground pipe system.

As i know very little of the technical side of these systems im looking for some suggestions of what to look at.
Also im told a co2 system is better than a system based on CFC's as it runns hotter and does not need the heaters to purge the system etc.

Thanks for any input.
James

Interesting to get your experience of this. I saw some literature on the Sanyo system earlier this year, and although the higher running temperature was attractive, the COP was not so good, meaning it was nearer 2 than 3+. Or have things improved?

Not sure why you were told "does not need the heaters to purge the system etc". Any system (CFC or CO2) that is undersized for low outdoor air tempertaures will need some backup.
You would be in an ideal position to keep your lpg for those extreme low temperature conditions when it could supplement an ASHP if you chose to size it for say -7 or -15 deg C.

A ground system could be better, but obviously an additional capital cost to install the pipes underground. Maybe £3k extra.

To be honest im not set on an air system, but would the 3k be over the cost of an air system?
re the heater point. I understand in cold extemees (ie -10 isnt common in the UK) that it may need the heaters to back it up. I was thinking of that legionaires issue.
Or am i missing that point? Does it still need to purge, or can it be left at a lower temperature (ie not 65 degs)?

James

Different refrigerants have a variety of properties that make them better suited to a particular temperature range or type of application than other refrigerants.

What properties does CO2 have that would make it better than other refrigerants for this particular application?

In the context of this discussion, what is meant by "purging"?

What makes a ground source system better?

Legionaires: I believe it is recommended to take the tank to 65 degC once a week. You would do this on a timer if the heat pump didn't have that process built in. So, running your normal daily hot water at 50-60 degC from the heat pump should be how it is done.

The heat pump unit would be similar in cost whether air or ground source. The cosst of the external ground works would depend on your situation and landscaping, but, yes £3k is an estimate which would be additional to the heat pump system.

Ok
so the equipment cost is similar between an air and a ground system, but the ground system has a much higher labour cost.
Are the running costs similar between the 2 systems?

Legionaires.
I see so does anyone know if the sanyo does this as std. The manual seems a bit poor. Its very hard to work out how to program it.

Potentially a small running cost benefit in favour of ground source because you have a stable temperature as your source which probably is always above zero. Ground source dosn't have to go through the periodic defrost cycle which air source has to go through in low external air temperatures.

You miss the point that the Sanyo CO2 system can produce hot water at 65+ degC, so it doesn't need an additional heat cycle.

However, as in my first post, look at the specification of COP at different temperatures. This will tell you the kw power used to produce output kw. Compare it with the best R410a models and you may find CO2 systems cost more to run than R410a at the moment. (relatively new development).

Ok thanks so far, wonderful info.
I iwll look into R410a as i have no idea at the moment what that is. I assume its a different Gas type.

So far im probably leaning towards an air system as the civil cost may be prohibitive for me.

I also think (and i may be wrong here) that the sanyo control system is restrictive and would prefer something i could connect to my home server or a pc etc. I would in time like to run it from a home automation system. It seems that i can only control the sanyo from inputs and outputs etc.

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Originally Posted by paceinternet

You miss the point that the Sanyo CO2 system can produce hot water at 65+ degC, so it doesn't need an additional heat cycle.

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Are you saying that other refrigerants cannot produce hot water at 65+C? Why not?

My knowledge is very limited but i thought that cfc based systems could not get much above 50 degress on their own and needed the electric heaters.

When i say 'purge' im meaning run the system to at least 65 degrees. I thought this was required due to legionaires. Maybe im using the wrong jargon and causing the confusion. Sorry if i am.

to add.
I assumed that CO2 was a good refrigerent in the uk due to our temp range, say -10 to +30
Outside of these is rare IMO, while we may have a night or 2 that drops to -18 its very rare.
I assumed (maybe wrongly) that it was cold temps that was a problem and hot temps didnt matter.

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Originally Posted by jameswilson

When i say 'purge' im meaning run the system to at least 65 degrees. I thought this was required due to legionaires. Maybe im using the wrong jargon and causing the confusion. Sorry if i am.

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Or perhaps its a euro thing. In any case, as long as I know what you mean, then we are on the same page and it isn't a problem.

I think from what i have read here is that CO2 can go hotter than 65 degs but some euro law prevents it? The settings let you but i assumed it needed electric to go hotter.

Gary. I agree best that all understand what im trying to say.
Should that system auto purge or do i need to set the water temp to 65 even in the summer.

Many Thanks again all
James

I have a quick Question. If I turn on my heat and it seemingly works fine...but when I go outside neither the fan on the air conditioner/heat unit or the heat pump are on is this a bad thing or what does it mean? I believe the heat pump is only for upstairs...

Are you saying that other refrigerants cannot produce hot water at 65+C? Why not?
Yes, why not, R134a and R417a can produce hot water at 65 degrees, in my opinion, ground source heat pump is very efficient, and you have plenty of ground to install underground collector system.

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Originally Posted by yangchenchen

Are you saying that other refrigerants cannot produce hot water at 65+C? Why not?
Yes, why not, R134a and R417a can produce hot water at 65 degrees, in my opinion, ground source heat pump is very efficient, and you have plenty of ground to install underground collector system.

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Three main reasons:
1. Condenser TD;
2. Compressor envelope restrictions;
3. Compressor discharge temperature.

It can be done, but you need to be careful.

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Originally Posted by desA

Three main reasons:
1. Condenser TD;
2. Compressor envelope restrictions;
3. Compressor discharge temperature.

It can be done, but you need to be careful.

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I’m sure the Altherma HT (air source) is a 2 stage cascade system, 410a to 134a and is capable of producing water temps >70 C.

^ That makes sense - it sorts out (2) & (3) in the list.

Many thanks for the information... :)

Calorex heat pumps have a variety of ASHP and GSHP available, the ASHP will run happily down at ambients of -15C, the refrigerant is R134a.

The system prioritises the water heating over the central heating of the house, all controlled by honeywell stat and controller. Hot water tank has independant stat, proper installs will have hot water tank with a separate buffer tank within the tank for efficient reverse cycle defrosting when required. The central heating fo the radiators comes directly from the unit instead of using a buffer tank.

I would go with GSHP despite the extra cost, less problems, no change in outside temperature/humidity to consider, cold foggy mornings are killing the ASHP spending lots of time in defrost, and the GSHP show some kick ass results.

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Originally Posted by jdunc2301

Calorex heat pumps have a variety of ASHP and GSHP available, the ASHP will run happily down at ambients of -15C, the refrigerant is R134a.

The system prioritises the water heating over the central heating of the house, all controlled by honeywell stat and controller. Hot water tank has independant stat, proper installs will have hot water tank with a separate buffer tank within the tank for efficient reverse cycle defrosting when required. The central heating fo the radiators comes directly from the unit instead of using a buffer tank.

I would go with GSHP despite the extra cost, less problems, no change in outside temperature/humidity to consider, cold foggy mornings are killing the ASHP spending lots of time in defrost, and the GSHP show some kick ass results.

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in relation to a lot of ground source units, i have noticed that on paper they run at a constant evaporating temperature higher than air source but once they are in i have found that a lot of installers are installing ground loops that are too small and the evaporators are running at temperatures within 2 degrees of the outdoor ambient.:eek:
I had a system last week, when the outdoor was -1 the ground loop was 0 degrees and the back up heater was also on at that time as the heat pump was undersized.
I do think that a larger air source system would be much more efficient as the outdoor ambient fluctuates.

Ground source is only really good for scandinavan countries where the ambients are well below 0 for most of the heating months.

each to their own opinions though..

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Originally Posted by brunstar

in relation to a lot of ground source units, i have noticed that on paper they run at a constant evaporating temperature higher than air source but once they are in i have found that a lot of installers are installing ground loops that are too small and the evaporators are running at temperatures within 2 degrees of the outdoor ambient.:eek:
I had a system last week, when the outdoor was -1 the ground loop was 0 degrees and the back up heater was also on at that time as the heat pump was undersized.
I do think that a larger air source system would be much more efficient as the outdoor ambient fluctuates.

Ground source is only really good for scandinavan countries where the ambients are well below 0 for most of the heating months.

each to their own opinions though..

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So... you are saying that GSHP's should be avoided because when improperly installed they don't work very well?

By that reasoning, we should avoid everything.

:D

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Originally Posted by Gary

So... you are saying that GSHP's should be avoided because when improperly installed they don't work very well?

By that reasoning, we should avoid everything.

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I though you might comment on this one :)

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Actually, I've become less tolerant over the years... lol

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Could that be less tolerant side :D

How's the weather in Florida? It's -8 C with 12" of snow in Scotland :rolleyes:
Not the best conditions for air source.

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Originally Posted by VRVIII

It's -8 C with 12" of snow in Scotland :rolleyes:
Not the best conditions for air source.

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Can make tepid water with that air... :D

Yuo can not simplify ASHP and GSHP.
Most closed loop GSHP are desighned to pump a fluid (glycol) at around 0 to -2C through the ground, using basic rules the SST would be around the -6 to -8C range, if we used this same SST for an ASHP the ambient would be around 0 to -2C (if we allow for defrost) +2C ambient, at this point performance would be the same.
If the ambient is higher than 2C on average then a ASHP is more efficient, if is lower on average then GSHP is more efficient.
So for NZ and most of the UK, the daily 24Hr avergae is higher than 2C so you should choose an ASHP.
The trick is then sizing the heat pump to meet strict heat loads at a specific tempearture,
For underfloor heating, I use a similar method of sizing, to how i would a coldroom.
Total energy over a 24hr period
devide by run hours (18hrs)
at a specific ambient (I use 2C)
This allows for defrosting, fluctuations in the daily ambient (normally below 2C at some part of the night/early morning and above 2C late morning/afternoon)
You can not use the nominal rating of the heat pump (as this is normally at 7C) you have to de-rate, if you are unable get manufactures ratings, reduce heat output by 2.5% per C drop in ambient.

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Originally Posted by mad fridgie

Yuo can not simplify ASHP and GSHP.
Most closed loop GSHP are desighned to pump a fluid (glycol) at around 0 to -2C through the ground, using basic rules the SST would be around the -6 to -8C range, if we used this same SST for an ASHP the ambient would be around 0 to -2C (if we allow for defrost) +2C ambient, at this point performance would be the same.
If the ambient is higher than 2C on average then a ASHP is more efficient, if is lower on average then GSHP is more efficient.

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What mean TD values are you using for the evaporator?
Does this value remain constant over the heating range?

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Originally Posted by desA

What mean TD values are you using for the evaporator?
Does this value remain constant over the heating range?

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I am using a "nominal" 6C, same for both, at the lower ambient (actual moisture content does not change massively) not as dramatic changes occur when compared to your high ambient conditions.
Like most things they could be designed better (both system).
Open loop GSHP normally have a higher SST, but need more power for pumping (unless is a lake)
To achieve best results, you need to move away from general heating rules of thumb.
Most heating using a boiler is short blast of high amounts of energy, hydronic heat pumps work better with a constant amount of energy being delivered, For example I only supply 30c hot water to the underfloor. My SCT are normally around 36C, of course you need to balance the expansion device for these lower pressure ratios (I use electronic wider operating range)

^ Thanks very much, MF.

It's very interesting to see how systems move around under these high ambient temp & high RH conditions.

We're in the middle of 'winter' with DB 32'C, RH 45%... :D

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Originally Posted by desA

^ Thanks very much, MF.

It's very interesting to see how systems move around under these high ambient temp & high RH conditions.

We're in the middle of 'winter' with DB 32'C, RH 45%... :D

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QUICK rush out and buy a snow shovel:D