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Author Topic: Cold and Hot Water from a Heat Pump? (Addition to Solar and Gas)  (Read 338 times)
sw25481
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« on: April 25, 2019, 10:08:55 AM »

I considered appending to https://www.navitron.org.uk/forum/index.php/topic,29785.0.html but my question is slightly different so I hope someone has some advice.

Can a single heat pump create both hot water and cold water but also have a fan and coil for when you have too much of either?


I have a very well insulated home that is pretty air tight, has MHVR, underfloor heating, etc. but also has a large outdoor pool that I heat for 4 months of the year (and a family that opens windows a lot to drive me crazy).  I have 8 of the largest Navitron Hot Water Solar Panels (4 pointing South East, 4 pointing South West) and they really help especially with the pool heating but they can provide much of my hot water and heating in the Autumn and Spring when not heating the pool.  However they are not enough and I still burn 40,000 KWh of Gas every year and feel pretty damn guilty about it.  In my machine room the panels and a 13KW boiler both feed a thermal store, underfloor heating and heat exchangers that heat the pool.  A Resol controller tries to do the right thing.

https://www.vbus.net/scheme/b36f04203aea2b958f6378b8358edd5b (Slightly simplified view)

I am thinking of getting a heat pump to reduce my gas consumption as I get my electricity from companies that only use 100% renewables.  I know it will not save me money but I feel if I only run it when it is warm it may not cost me too much I am just not convinced offsetting my carbon is enough.

However last summer I had so much trouble sleeping in the heat I am about to buy and install a few of the easy fit air conditioners.  Mostly for cooling on the very hot days, but I also rationalised I may be able to keep the rooms at a slightly lower temp in Spring and Autumn perhaps just from Solar knowing I could pop one on for a little heat.

What pains me is having one heat pump making waste cold air to heat the pool and several heat pumps making waste hot air to cool the rooms.  I just can't help feeling there should be a better integrated system.  I am also frankly worried about having to upgrade to 3 phase to run them all.

Can a single heat pump create both hot water and cold water but also have a fan and coil for when you have too much of either?

On an ideal day I could feed the hot water into my pool (either directly or via my solar heat exchanger) and the cold water I could use to cool my house (perhaps by pumping it round my underfloor heating or if it was easier just using a standard fan driven evaporator like on any split air con system).

If the house is already cool enough but the pool needs heating I would want the air handler to act as a condenser coil dump the waste cool air.  Probably less likely if the pool is warm enough but the house needs cooling I would want the air handler to act as an evaporator dump the heat.  Plenty of Heat pumps will work in either mode but they only seam to provide hot or cold refrigerant or hot or cold water (if they have built in heat exchanger)

I can't get over the feeling that if we were not talking about greenhouse gas this would be a simple plumbing challenge no more complex than most of us have dealt with Water Heating Solar panels.  My pool water heat exchangers, boiler feeds, solar feeds are all within a few meters of each other.






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Countrypaul
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« Reply #1 on: April 25, 2019, 11:08:36 AM »

It sounds like you are looking at the wrong sort of heat pump. Try looking at Ground source heat pumps (also sometimes called water source heatpumps) as these normally pass water (well brine) around a loop in the ground (or pond, river etc) to obtain the heat and output the heat to water to produce hot water for heating or even DHW.
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pdf27
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« Reply #2 on: April 25, 2019, 06:09:37 PM »

That sounds vastly over-complicated, and probably not actually very efficient. Just get yourself a simple swimming pool air source heat pump and run it in parallel to the existing system. Costs are pretty modest (Navitron don't do a suitable one and I'm not going to link to the competition, but you're not looking at much above 1k for a 13kW model) and because the water temperature is pretty close to the air temperature you're likely to see COPs in the region of 5-6 which should make things cheaper than gas for most people.

Extracting heat from the house to heat the swimming pool is one of those ideas that sounds great in practice but is a nightmare in reality - 95% of the time the numbers just won't add up, and worse you're likely to end up with a system wrongly sized for a large part of the year. Worse, pumping heat from house to pool may not actually be any more efficient than pumping from house to air and air to pool - the centre temperature is the same, so you're only losing out on the efficiency of the extra heat exchanger which is probably a pretty small effect.
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