Advice on commissioning ASHP - UFH system

[lenny]

Hi
when commissioning a Air/water heat pump for UFH via an accumulation tank on a large system (200m2) Is it best to start with a low flow temp to the UFH then gradually increase the temperature. If this is correct ?. What temperature should be introduced first? At what temperature should it be increased to? How often should it be increased?

The system is calculated on a flow temperature of 40 degrees , , the problem I've had is setting the flow temperature at 40 degrees , this completely robbed the hot water from the tank due to the low return temperature from the UFH, then the ASHP seems to struggle to keep up with the demand.

Hope this makes sense and any comments and advice would be appreciated.

Len

 

[Worcester]

#0) What is the make and model of the heat pump?
#1) What is the heat load (kW) and what is the A2/W35 Rating of the Heat Pump?
#2) What size is the Buffer (Accumulator) Cylinder?
#3) What ΔT and flow rate is the UFH designed at
#4) What ΔT and flow rate is Heatpump set at?
#5) Which make and model / version manifolds are you using for the UFH?
#6) What sensors do you have in the buffer cylinder?

Given that info, then we can start to answer, else we haven't a clue what might be going wrong.

Though I would first check a) blending valves and b) flow rates on the UFH, get those set up first...

 

[lenny]

Hi

thanks for the reply.

the heat pump is a CTC Eco air 120.
a2 / w35 = heat output 14.91kw , power input 4.39 , COP 3.4
heat load 28kW
1000ltr AKVA geo tank
40 degrees , all flow rates set to underfloor heating design
set to the max at 64 degrees , it is not direct but via a coil in the lower part of the AKVA tank.
IVAR combimix manifold

The AKVA tank has a domestic hot water coil which distributes domestic hot water to 3 bathrooms and a kitchen . there will also be a wood boiler fitter at a later date , which will produce 16kw to the water / accumulation tank and 10kw to the room it is in. The system also has 6m2 of solar thermal panels .

hope this helps! Thanks in advance

len

 

[lenny]

Ooops sorry before I get shot down the heat load is 18kw not 28kw

thanks

len

 

[Ermintrude]

Would start at 20c and raise in 3c increments every day if screed is wet. (7 days or older)

 

[lenny]

Morning and thanks for the reply, the screed has been down for 5 months

len

 

[Nostrum]

Hi
when commissioning a Air/water heat pump for UFH via an accumulation tank on a large system (200m2) Is it best to start with a low flow temp to the UFH then gradually increase the temperature. If this is correct ?. What temperature should be introduced first? At what temperature should it be increased to? How often should it be increased?

The system is calculated on a flow temperature of 40 degrees , , the problem I've had is setting the flow temperature at 40 degrees , this completely robbed the hot water from the tank due to the low return temperature from the UFH, then the ASHP seems to struggle to keep up with the demand.

Hope this makes sense and any comments and advice would be appreciated.

Len

How long was it running for? You'll need to allow the slab to warm and then the room temp to raise before the heat pump will be able to start accumulating heat in the store. Sounds like the heat loss exceeds the heat pump output at the moment.

 

[Worcester]

Definitely undersized (at the moment), i.e. heat loss exceeds supply.

With an 18kW load from cold the heat pump is going to struggle, based on the design you've got an undersized heat source until the wood boiler is commissioned, (I wouldn't budget on much heat input from the solar at this time of year !)

To stand any chance , you're going to need the get the buffer up to full temperature before you start loading the UFH, and then i'd do it zone by zone, starting as suggested by setting the blending valves down at 20C and then raising a few degrees every couple of days, keeping a close eye on the buffer temperature. Presumably you've got multiple stats in the Akva tank - so keep an eye on those.

Even 1000ltr has only got a store of 23kW at a ΔT of 20° (45 down to 25) so if your heating a load of 18kW from a 'hot' store and no source, it's only going to last 1hr 20mins...
(a 4KW shortfall and with the HP at full output, from hot the store will be depleted in 6 hours under NORMAL running conditions let alone start up....)

Makes sure the ASHP is on 24/7 and the same with the UFH

The UFH screed will also act as a buffer (thermal mass) when it's finally up to temperature, however until then it's going to soak up every watt you can throw at it!

Seeing as we've had one of the coldest spells for a while you've got an uphill, maybe impossible struggle until the other heat source is commissioned.

 

[Nostrum]

The air source sounds like more of a supplement on this system then? If your expecting DHW from the store then your going to need to use the immersion to raise 1000litres by 20 degrees if just using the heat pump?

I take it the wood burner will heat the store to 80 and then the UFH circuit can blend it down meaning you can store much more energy in the store?

Is there a reason for installing the pump first rather than the wood burner? Sounds like an interesting job though.

 

[Nostrum]

Also, Worcester, how do you get the delta symbol to work?

 

[Worcester]

Also, Worcester, how do you get the delta symbol to work?

Copy and paste from word (Alt+0916 in word ) Or Insert Symbol

 

[lenny]

Thanks for the advice and your time, I will give it a go.

len

 

[chris watkins]

Would it be worth getting in some (hire ?) supplementary heating, either to raise the rooms (floor) temps or direct into the buffer, what would be best ??

 

[Worcester]

Until you add in a full time additional heating source, the moment you turn off the supplementary heating the property is going to cool down and the heat pump won't cope

You should immediately commission an interlocked bi-valent system else just switch the heat pump off and put in a heating system that can cope.

Presumably the buffer tanks has been commissioned with multiple inlets temporarily blanked off with full bore isolating valves?

If so it's simples, first question - what fuel sources have you got available on site?

(What was there before someone made the mistake of trying to get an undersized heat pump to work in winter with an icy balst predicted tommorow )

pm me or call me - you can get my details from my website in my signature below.

Seems like you need a problem solver to make a site visit and agree a fix with the client else they are going to be going into Christmas with a frozen turkey for lunch...

 

[Ermintrude]

Until you add in a full time additional heating source, the moment you turn off the supplementary heating the property is going to cool down and the heat pump won't cope

You should immediately commission an interlocked bi-valent system else just switch the heat pump off and put in a heating system that can cope.

Presumably the buffer tanks has been commissioned with multiple inlets temporarily blanked off with full bore isolating valves?

If so it's simples, first question - what fuel sources have you got available on site?

(What was there before someone made the mistake of trying to get an undersized heat pump to work in winter with an icy balst predicted tommorow )

pm me or call me - you can get my details from my website in my signature below.

Seems like you need a problem solver to make a site visit and agree a fix with the client else they are going to be going into Christmas with a frozen turkey for lunch...

I can rent u a trailer with 400kw of heat 100ft of 4" hoses and a twin head pump? if any good?

 

[chris watkins]

I can rent u a trailer with 400kw of heat 100ft of 4" hoses and a twin head pump? if any good?

He wants to heat the house Ermi, not bl**dy cook that turkey. LOL

 

[Nostrum]

Or just zone off one side of the house and hope the heat pump can cope with the other half. Maybe bypass the store as well as the UFH will need to be on 24/7 anyway.

 

[Worcester]

Or just zone off one side of the house and hope the heat pump can cope with the other half. Maybe bypass the store as well as the UFH will need to be on 24/7 anyway.

I remember as kids when we had 't scrape ice off ta ba'room winda's ....do em good Nowt a couple of jumpers and a good log fire can't cure (and a hot mug of cocoa) :xmas::carolers: