Choosing the correct Central heating Pump

[mpooley]

Hi all
I have a large house that used to have very poor circulation to the furthest rads in the system. A plumber installed a much larger pump and told me that would sort out the problem.
It didn't.

I eventually had lots of floorboards up and found out that the whole system was using 15mm pipe - It left the pump and was fed with 22mm pipe downstairs to a sort of home made distributor but before it reached this it went down to 15mm which seemed crazy to me.

I sorted this out myself and then replaced as much of the 15mm pipe with 22mm as I could.
This did work !
Now I am changing over to a ASHP with low water temperatures that will be running 24/7. The pump seems to use a lot of power even though I have it on the lowest setting so Having it on 24/7 will cost a lot in electricity.
Hence me asking this question.

My present pump is a grundfoss 3 speed type UPS 25-80 185.
I would like to replace it with an A rated low energy pump.

How do I work out what size of pump I need?
is it number of rads or total size of rads ? something like that?

Oh and do you recomend the Grundfoss Alpha 2 ?

thanks in advance

Mike

 

[Corgigrouch]

Well if you are bothered by the electricity that your pump uses, you'll have a fit when you get your electricity bill after running the airsource..

I think that unless you look closely at the design of your entire heating system then the ASHP will dissapoint you

 

[mpooley]

Well I am expecting a huge rise in electric use of course.
My investigations and experiments tell me that my system will work well at 45c and compared to my current oil bill it should be significantly cheaper to run

I asked about the pump as I don't like to waste money on a poorly sized inefficient one.

Mike

 

[Corgigrouch]

I must admit that I don't like these variable speed pumps, mainly because the control part of them can give problems and a step down from your 25 80 to a little alpha2. Do you really intend to leave your heating on 24/7?

 

[mpooley]

Yes I am retired and we are at home all day.
I ran my heating at 40-45c all winter as a test to see if the ASHP would be able to heat the house Ok and we found it was best if we ran it 24/7 with a slight setback at night. Also we could set the stats lower as the Temps in the house were so even.
Actually the house has never been so comfortable.

It didn't seem to make much difference in oil use either. except that this winter was a bit long.

thanks

Mike

 

[Corgigrouch]

That is an unusually cool water temperature but I can see your logic in running it 24 hours.... I would suggest that you keep your oil system linked to your system for when the air source can't cope in the cold weather.... Snow and freezing fog knocks them for six and that you install a buffer vessel so enough energy is stored to allow the system to defrost properly without your rads cooling..

 

[mpooley]

They say that the lower the water temp the more efficient the Heat pump works.
I found that my system without larger rads needs about 45c which is should give me a COP of 3 on average. (hopefully)

Oh and I will be keeping the oil boiler for just those reasons. for a few years at least.