UPDATE ASHP OR GET GAS

[PeterW]

6 minutes ago, ST3VE78 said:

There are 2 pumps in the drawing.

  
Circulation pumps not heat pumps - where is the circulator in the house ..?

 

6 minutes ago, ST3VE78 said:

I can have one to go off at say 30 when it’s warm out and the other will take the water to 35+ easy. I think I’ve been sold a duff system by the look of it. 

Right … I think you have a flow issue and what’s happening is that one pump is doing most of the work - they aren’t piped in tandem from that picture they are in parallel. What should happen is that one does the first heat input (say 25-30°c) then the second then does the  uplift from 30°C up to the set temperature. What you’ve got is a single circulator pushing into a pair of heat pumps and it will favour the one with least resistance - if one is cutting out then I would think it has low flow through it and is seeing a set temp before the other.

 

A single 16kW heat pump would make it a lot simpler and I would think you’d get a lot better function from it. 

[ProDave]

15 minutes ago, ST3VE78 said:

No is the answer Dave. They have always struggled when the outside temperature drops. When it’s warm out your feet are toasty on the ufh.

That worries me, as between them you should have 13kW of heat available and my worry is your house needs more than 13kW of heat.  i would hate to advise you get a new ASHP only to find it behaves no different.

 

2 hours ago, ST3VE78 said:

When my architect completed the SAP he said space heating kWh per year 21,158

That is a high number.  But annual total is not very helpful.  VERY rough sums, you use all that heating need in half the year, so 180 days per year, so 117kWh per day average.  Now lets assume the coldest day is twice that, so 234 kWh  so if the heating was on 24/7 that would be 9.75kW  so your two ASHP's should be able to manage that.

 

It is a shame you cannot find a competent engineer. Even if they are not a heat pump expert you should be able to find someone to analyse what is going on with some basic temperature measurements and experimenting. 

 

@PeterW is on the right lines, any competent engineer with a thermometer and a clamp ammeter (to see how much power each heat pump is consuming) and some observation should be able to see if it is just one working or both and get a handle on what is going on.

 

I would hapilly look but I am not making a 1000 mile round trip.

[ST3VE78]

I’ll look at getting 1 bigger modern one I think.  I just think these pumps are not designed to handle the cold weather. Even if I only turn 1 room on the flow temp stays low.  It’s 8 degrees out now and the floor has warmed to 40 degrees no problem and it’s toasty here with room stats on 20. Heat pump have turned off too. Below 3 deg and I may as well turn them off and plug in electric blow heaters ☹️

[ProDave]

1 minute ago, ST3VE78 said:

Even if I only turn 1 room on the flow temp stays low.

I would want to be SURE that really is the case before spending money.  I find that hard to believe as you should have 13kW available at air 0 water 35.  Unless they have been "faulty" right from new.

[PeterW]

1 hour ago, ProDave said:

I would want to be SURE that really is the case before spending money.  I find that hard to believe as you should have 13kW available at air 0 water 35.  Unless they have been "faulty" right from new.

@ProDave read my explanation - I doubt the way it is set up it will deliver 13kW. It should have 2 pumps and a set of non-return valves.  

[ST3VE78]

I can see one pump for the DHW and another after the buffer for the ufh. Both on the flow side. These are both bigger compared to the ones on the manifolds. I can’t see how this would stop the heat pumps getting out of the 20’s when it’s cold out tho. Above 5 degrees the system works well.

 

[PeterW]

2 hours ago, ST3VE78 said:

. I can’t see how this would stop the heat pumps getting out of the 20’s when it’s cold out tho.

because at 5°C one pump is fine !! And you have got inequal flow through the pumps as they haven’t been properly balanced and doing parallel pumps is a really bad idea !! 
 

2 hours ago, ST3VE78 said:

can see one pump for the DHW and another after the buffer for the ufh

ok that sounds worse than before !! It should be a single pump on the return (they last longer, it’s cooler) but what I can see from what you’re saying is that you have variable flow depending on the  destination of heat.

 

single ASHP, pump on the return and wired properly for W plan, this will all work much better than you have today.