Thanks @jamespa I will.

Posted by: @pipebaron

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Long time listener and new to the forum. Currently using a combi but experimenting with low temp heating and looking at ways of improving my system.

 

im currently getting quotes for a heat pump and cylinder installation and very much into the technology now.

Happy to emeet you. We will eventually go the same way, from a combi to a heatpump and so interested in what's forcing everybody to get a cylinder back in for the pumps. We have a cold water pressurized cylinder so the combi can cope with two showers running. Do not like the idea of preventing legionella etc. Will keep an eye for that thread!   

Posted by: @batpred

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interested in what's forcing everybody to get a cylinder back in for the pumps. We have a cold water pressurized cylinder so the combi can cope with two showers running. Do not like the idea of preventing legionella etc. Will keep an eye for that thread!   

The cylinder is there because heat pumps are 'low and slow' - they can't do bursts of high heat output, so you have to heat the water over a period of time (about 30-40 minutes for my 200L tank), and store it so it is ready for use when needed. It works fine, unless you have exceptionally high hot water use, in which case you might need a larger tank. The DHW tank also needs to be a heat pump compatible one ie have a larger heating coil inside, in just the same way radiators need to be larger.

The legionella cycles are optional. The actual risk in most domestic settings is low, and assuming no other risk factors eg immunocompromised residents, then it is entirely up to you whether you use them or not.

Posted by: @cathoderay

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The DHW tank also needs to be a heat pump compatible one ie have a larger heating coil inside

or

• you can add a circulator pump and PHE (instead of the coli) to re-use an existing cylinder with an ASHP
• in some cases, particularly if you have an R290 heat pump, you will be able to reuse an existing cylinder with its existing coil with an ASHP if you accept a performance penalty.  The payback time might be very long if you can heat your DHW at cheap rate, so this and the above are well worth considering if you have a fairly new UVC.  

Posted by: @cathoderay

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Posted by: @batpred

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interested in what's forcing everybody to get a cylinder back in for the pumps. We have a cold water pressurized cylinder so the combi can cope with two showers running. Do not like the idea of preventing legionella etc. Will keep an eye for that thread!   

The cylinder is there because heat pumps are 'low and slow' - they can't do bursts of high heat output, so you have to heat the water over a period of time (about 30-40 minutes for my 200L tank), and store it so it is ready for use when needed. It works fine, unless you have exceptionally high hot water use, in which case you might need a larger tank. The DHW tank also needs to be a heat pump compatible one ie have a larger heating coil inside, in just the same way radiators need to be larger.

Our situation is I will not embark on getting a heat pump for a long time, we are still managing the much simpler install of a battery and inverter! 

Just thinking aloud, a pump that could do away with the tank would have to deliver 15kw+ heating as a minimum, I am guessing. Considering that the efficiency may drop at some points, it would be a matter of knowing the worst instant efficiency it will need to work at to be able to know what the electrical power of the pump would be. And of course a small built-in tank is essential for instant hot  water and to avoid constant stop start. So something like the Grant Aerona R32, 17 Kw, would do, this has a minimum flow rate of 15 l/min, sound power level of 61db at 1m, 32 Amp single phase input, but it seems to draw less than 5Kw. Pumps would not need to operate at less than 2 COP/efficiency in SE England anyway. 

So it is possible but clearly since the air is going to be warmer in the middle of the day, storage for the heating will make a big difference in efficiency... Given the temperature fluctuations over 24hrs, having a heat storage adds some complexity/risk of failure and requires space but will reduce consumption.   

@batpred Might be worth looking at the Heat Geek options for DHW tanks; they offer a few options including one akin to a gas boiler instant supply. Regards, Toodles.

If you know what you need the maths is straightforward.  Assume water in is at 10C and shower water at 40C.  The heat capacity of water is 4.2kJ/lC

So for each l of shower water you need 30*4.2kJ = 126kJ

This to deliver 1l/min you need power of 126/60 = 2kW.

So 2kW per litre per minute.

Now define your flow requirement and you can work out the power needed.

@batpred - putting it another way, why not have a DHW tank, unless there is an over-riding reason? Heat pump variants mesh well with the way a heat pump works, they 'just work' and unless you have exceptional shower requirements, then you can fit a tank with sufficient capacity to supply what you need. In contrast forcing it to behave like a combi boiler rather flies in the face of the way heat pumps work best.

Posted by: @cathoderay

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@batpred - putting it another way, why not have a DHW tank, unless there is an over-riding reason? Heat pump variants mesh well with the way a heat pump works, they 'just work' and unless you have exceptional shower requirements, then you can fit a tank with sufficient capacity to supply what you need. In contrast forcing it to behave like a combi boiler rather flies in the face of the way heat pumps work best.

I suppose as the heat pump transfers heat from the outside in, it gets more heat per energy unit whenever it is warmer outside so unfortunately some of the boiler flexibility goes with it  For us, the main challenge is to find space for the tanks. But of course anything that is another part of the solution needs care and attention and can break and specially when not integrated in the original solution, break without much notice. 

Posted by: @batpred

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For us, the main challenge is to find space for the tanks.

I've seen photos of other people placing the tank in a highly-insulated 'shed' outside the house.
The shed was sited so that the pipework could enter straight into the house in a 'useful' position.

You'd need to provide more detail on the layout of your particular property (in a separate topic and with photos please),
but don't put it past the combined brain-power on this forum to come up with a workable solution!  😀 

Hi, not sure if this is a UK only forum, I am living in Estonia so before I start picking peoples brains I should ask if location matters? Thanks

Quite the opposite, @chris12. We don't care where someone is based and if we can help then you're very welcome to join us.

The only issue is whether I have brains to pick, but I do know for definite that there are certainly brains here worth the effort.