ASHP is the power of the water pump enough for the radiators?

[keyser]

Sounds like a daft question but I will still ask it  I'm used to a fair amount of noise when the gas boiler comes on and a part of that noise is the water pump for the radiators. I like things quiet! I take it all the noisy parts will be outside if I had an ASHP monoblock? The water gets actually pumped from the pump inside the monoblock and nothing else? Then a diverter kicks in sometimes to heat up the hot/warm water tank? Thanks

[PeterW]

Depends - some have the pump inside but I only spec / fit Wilo now so noise is irrelevant. They are quieter than a church mouse farting 

[keyser]

Ah yeah that makes sense, finally people realise quiet things are a good idea, thanks.

[ProDave]

I had to fit a second pump inside the house because I could not get enough water flow rate to keep the ASHP happy.  If you are determined it will run entirely on the outside pump, then plumb accordingly, i.e. 28mm main flow and return to start with (mine is only 22mm)

[JohnMo]

a pump should not be noisy, air in system, or lack of pressure upstream will cause cavitation which will make a racket.  Also a gas boiler should be near silent.

[ReedRichards]

I have a second pump inside my house for the central heating because that is the way it was fitted for me.  The pump itself is not particularly noisy although audible outside the airing cupboard where it lives.  But noise from water circulating in the pipes close to the pump is more of a problem.    

[keyser]

Thanks, I suppose the noise tolerance is different from person to person is a factor as well. I'm on the fussy end of the spectrum. The fridge freezer will be a quiet one the next time it's changed - it's secondary job is to cool things :). Maybe the gas boiler is making slightly more noise as its 10 years old now. When each noise is eliminated it just reveals the next loudest noise. The gas boiler/pump isn't loud but I can hear it for sure, I just want to make sure if my radiators are on 24/7 with ASHP in the winter I won't be bothered about the noise.

[TW9]

I have four circulation pumps on my system. Is that too many? 😁

 

[JohnMo]

Bit of a random question, without any specific details?

[m0deller]

We have 3 pumps , 2 inside (Wilo and Grundfos) and 1 in the external unit. This is due to having the Vaillant HEX module. 

[dave 57]

Our new ASHP system is fitted with a Grundfos UPS3 (modern 4 bedroom detached). It was set on the highest constant setting, 3. Would I be able to run it in Proportional-pressure mode I, II?

If I placed it in this mode , what would I look for to check it's success or failure?

thanks dave

[ReedRichards]

If water is circulating too slowly the temperature drop across your radiators will be larger than specified.  For heat pumps the specified temperature drop is typically 5 C; I presume this is just so the average radiator temperature does not fall too low.  On the other hand there are modern gas boilers that seem to target at 50 C flow and 30 C return so a much larger temperature drop requiring radiators with a larger surface area.  I don't understand why there should be such a disparity between low temperature gas boilers and heat pumps.  

[Miek]

8 hours ago, ReedRichards said:

 On the other hand there are modern gas boilers that seem to target at 50 C flow and 30 C return so a much larger temperature drop requiring radiators with a larger surface area.  I don't understand why there should be such a disparity between low temperature gas boilers and heat pumps.  

For a condensing gas boiler the latent heat recovery is more efficient the lower the return temperature.  

[RobLe]

An ashp heatexchanger has an f-gas or similar undergoing a phase transition at constant pressure, hence constant temp.  If the flow of water is so slow that you get a 20C deltaT, I think the phase transition will have to occur at the hottest temp of the water (neglecting superheat), so the cop won’t be as good as at a higher water flow limiting that temp.
Gas boiler energy transfer is not dominated by a phase transition so it’s the return water temp that counts, so a bigger deltaT is ok and won’t hurt the efficiency so much.

I think.

 

[JohnMo]

Even a gas boiler doesn't need or want a 20 deg delta T. at low temps. I'm running mine for UFH and its modulation gives 6 degree delta. If it running at about, 25 degrees there is only a 3-4 delta.