How to set up my ashp

[Pete]

I have had my heat pump on now for over a week and it does seem to be working a lot. I know the house has a large footprint (predominantly g/f with only one room upstairs) but I am unsure how to set it up for the long term. I know @jackhas a similar heat pump and he uses the weather comp curve instead of the direct setting but is this the norm? I had mine set up in the direct mode to start with but changed it later to the comp curve just to see if the amount of time the pump was running was reduced but if anything it has increased the pump running times. I understand each house is different and with this cold spell the house will need more heat to sustain the internal temp but what have people set theirs to? Have you got worked out a more efficient way of running your heat pump? If I was to go onto E7/E10 then I am not sure that there would be enough time to heat the house in the time aloted for the reduced rate of electricity. At the moment I have my heat flo temp set to 35 down to 30 and the outside temp setting -5 to 15 as I tried what @jack (30 and 25 and 0 to 7) had his set to and the house was not getting warm. 

The house is Passive with ufh pipes laid at 200mm and is all one zone. At the moment I am not sure whether I should have had closer pipe centres to increase the heat output or whether due to the larger footprint my heat load will always be high OR whether my settings need changing to work better? The system is run by a room thermostat set at 21 and the house is lovely and warm so I know I could lower the temp but when you are sitting it can get quite cold. I have had a look at the power consumption and I used 52kw yesterday, 37kw day before and 31kw before that but the weather has turned colder these past few days and the average COP is 2.2. 

I seem to recall that people run their pumps in segments throughout the day but I cannot do that as the house would not be warm enough. Do I increase the output flow temp to heat the floor quicker(?) or is that not the correct approach as I am then reducing the efficiency of the heat pump but would the heat pump not run as long? I know some people run their heat pump using the buffer tank instead of a room stat but not sure if this would help me? 

Any advice or insight into how people run their heat pumps would be greatly received as at the moment my elec bill is on a steep upward spiral!! TIA

[ProDave]

If the house is really passive house levels I am surprised it is strugling.

 

But there's some conflicting information there, e.g. the house is at 21 degrees and lovely and warm,but you feel cold?

 

Our room stats are set at 20 degrees and that is indeed what the living room is at just now, but at different times of day you might feel hot or you might find that a bit cool. It depends what you are doing.

 

Our UFH comes on at 6AM and by 9AM the room stats have clicked off and probably won't come on again for several hours just to keep it topped up.

 

Are you including DHW in your energy measurements?  You might well find the ASHP uses as much to heat the HW as it does to heat the house.

[Pete]

14 minutes ago, ProDave said:

If the house is really passive house levels I am surprised it is strugling.

 

But there's some conflicting information there, e.g. the house is at 21 degrees and lovely and warm,but you feel cold?

 

Our room stats are set at 20 degrees and that is indeed what the living room is at just now, but at different times of day you might feel hot or you might find that a bit cool. It depends what you are doing.

 

Our UFH comes on at 6AM and by 9AM the room stats have clicked off and probably won't come on again for several hours just to keep it topped up.

 

Are you including DHW in your energy measurements?  You might well find the ASHP uses as much to heat the HW as it does to heat the house.

I tried to include as much info as possible but it sometimes gets things all  mixed up. Now it is 21 degrees it is lovely and warm but when we had it at say 20 it felt cool at times. 

If I set my heating to come on at 6 to 9 it would not heat the house but my house is obviously different to yours Dave. What have you got your settings at for the heat pump to deliver hot water for the heating and it must be direct if on set times?

My figures do include the hot water so I realise my usage is not all heating.

The large kw usage was the first time I used my large bath so that accounts for the high usage here!!

Edited January 1, 2021 by Pete
To add more information

[joe90]

Is the house newly finished?, if it is I believe it will take quite a while for the fabric to heat up, luckily our was finished at the end of winter so spring temps helped but I ran the UFH for weeks (on immersions ?) to get it up to temp, then I got the ASHP working.

[Pete]

1 minute ago, joe90 said:

Is the house newly finished?, if it is I believe it will take quite a while for the fabric to heat up, luckily our was finished at the end of winter so spring temps helped but I ran the UFH for weeks (on immersions ?) to get it up to temp, then I got the ASHP working.

I must admit I have committed to memory to move in spring/summer next time I self build (NOT). It is a fine line of wanting to feel comfortable when just sitting and not feeling a tad chilly now I am no longer a young whipper snapper. I will be a little disappointed if I have gone to the trouble of achieving .4 air test (with known air leak in missing window trim which is now in) and spending my money on a well insulated house to think my elec bill will be quite large. I think I also need to accept that the house is quite large in volume so common sense tells you it will take some heating. The problem I am trying to sort out is how to control it as at the moment the pump is just left running otherwise the temp setting on the stat will not be reached by just doing the heating in chunks. I know it is early days as I have had to heat the house up from cold and the temp outside has been -4 so the pump is working overtime at the moment.

[ProDave]

What make and model of heat pump?

 

Some (not all) let you set different flow temperatures depending on whether is is doing space heating or how water heating.  You probably want the flow temperature about 35C when it's doing space heating, and not much more than 50 degrees for HW.

[Pete]

12 minutes ago, ProDave said:

What make and model of heat pump?

 

Some (not all) let you set different flow temperatures depending on whether is is doing space heating or how water heating.  You probably want the flow temperature about 35C when it's doing space heating, and not much more than 50 degrees for HW.

It is a Panasonic Aquarea 9kw and the flow temp is set at a high of 35 for heating and 48 for HW.

[jack]

Not sure what else I can say. I use weather compensation that sets a flow temp of:

• 25°C when the outside temp is above 7°C
• 31°C when the outside temp is below 0°C 

It ramps in a linear way from 25°C to 30°C as the outside temperature falls from 7°C to 0°C.

 

Our pipes are on 200mm centres like yours.

 

I find this keeps the house perfectly warm. If anything, it's been a little too warm after these last few very cold days, and I'm thinking of tweaking things slightly so that we get slightly lower flow temps at lower outside temps.

What are your floor coverings? We have polished concrete over nearly all of our downstairs floorplan, which does make heat transfer quite efficient. The carpeted TV room can be slightly cooler than the rest of the downstairs area if no-one's in it.

 

Also, it's true that a single storey house will tend to use more energy for the same floor area. 

 

Another thing to keep in mind is that there's nothing wrong with the unit running for longer periods of time. Yes, there's wear, but I don't know that there's any less wear running it for a shorter period of time if you're running it harder to run a higher flow temperature.

 

[Pete]

5 minutes ago, jack said:

Not sure what else I can say. I use weather compensation that sets a flow temp of:

• 25°C when the outside temp is above 7°C
• 31°C when the outside temp is below 0°C 

It ramps in a linear way from 25°C to 30°C as the outside temperature falls from 7°C to 0°C.

 

Our pipes are on 200mm centres like yours.

 

I find this keeps the house perfectly warm. If anything, it's been a little too warm after these last few very cold days, and I'm thinking of tweaking things slightly so that we get slightly lower flow temps at lower outside temps.

What are your floor coverings? We have polished concrete over nearly all of our downstairs floorplan, which does make heat transfer quite efficient. The carpeted TV room can be slightly cooler than the rest of the downstairs area if no-one's in it.

 

Also, it's true that a single storey house will tend to use more energy for the same floor area. 

 

Another thing to keep in mind is that there's nothing wrong with the unit running for longer periods of time. Yes, there's wear, but I don't know that there's any less wear running it for a shorter period of time if you're running it harder to run a higher flow temperature.

 

Floor covering is Porcelain tile throughout so no problem there. With the unit running a lot it is defrosting frequently as every time i go outside it is defrosting so tend not to go outside to much!!

[jack]

Just now, Pete said:

With the unit running a lot it is defrosting frequently as every time i go outside it is defrosting so tend not to go outside to much!!

 

Lower flow temps should in theory reduce how often you need to defrost - another reason that it can be better to run at a lower flow temperature for longer.

 

Bear in mind how defrosting works: you pump a load of heat into the slab. When you need to defrost, the unit sucks some of that heat back out of the slab to heat up the fins and melt any ice that's built up. This is one contribution to the fall in COP as the outside temperature falls towards zero. 

 

I genuinely don't know how different things will be if you just run it 24 hours a day at, say , 28°C versus shortened periods at, say, 35°C.

 

Some form of monitoring would help you see what's going on. I don't know whether you can access it via your controller, but the one that came with my Aquarea lets you see lifetime energy for heating and hot water generation as separate kWh figures. You could record that number in a spreadsheet every morning or evening along with the average or peak temperature, and see whether you can draw any conclusions over time.

[SteamyTea]

First things first.

It is kWh, not kw, or KW, or Kw.

 

Second point, raising the flow temperature should heat the house quicker, energy transfer is proportional to the surface area, shape and temperature differences.

 

Thirdly, is your house really a PassivHaus, or built to a similar standard? How much insulation, and what type is under the floor?

 

Fourth point, is your ASHP actually defrosting, or just stopping?  This may because of short cycling because you are running it at a higher temperature.

 

Fifth point, is the ASHP the right size?  The efficiency drops as you reach its maximum power (power is kW, not kWh).

[joe90]

Mine is running more in this cold snap, but yet to see it defrosting ?

[ProDave]

I am pretty sure it has been colder this last week here than with any of the rest of you.  I have just done my weekly meter readings and in the last week used 60kWh on heating and 29kWh on DHW

 

Re defrosting, I don't think I have ever seen mine do that when space heating, it only does it when heating DHW.  It is pretty clear to see if you witness it.  you hear the compressor slow and stop, a click and a whirr as the 4 port valve reverses, the compressor starts up this time taking heat from the house and heating up the fins.  It only takes about a minute and as the ice melts you see the cloud of "steam" puff out.  then the compressor stops, the 4 port valve reverses again and it starts up normally again.  It does push up the DHW usage as the COP will be lower, last week when it was less cold we only used 25kWh for DHW

 

What analysis have you had done on your house to predict the actual heating requirements?

[Pete]

2 hours ago, SteamyTea said:

First things first.

It is kWh, not kw, or KW, or Kw.

 

Second point, raising the flow temperature should heat the house quicker, energy transfer is proportional to the surface area, shape and temperature differences.

 

Thirdly, is your house really a PassivHaus, or built to a similar standard? How much insulation, and what type is under the floor?

 

Fourth point, is your ASHP actually defrosting, or just stopping?  This may because of short cycling because you are running it at a higher temperature.

 

Fifth point, is the ASHP the right size?  The efficiency drops as you reach its maximum power (power is kW, not kWh).

I know it is kWh.

Yes the house is Passive just not certificated. 400mm Eps in the slab, walls 300mm and warm roof 400mm.

I assume it is defrosting as the fins are covered in ice and then they are not!!

 

[Pete]

1 hour ago, ProDave said:

I am pretty sure it has been colder this last week here than with any of the rest of you.  I have just done my weekly meter readings and in the last week used 60kWh on heating and 29kWh on DHW

 

Re defrosting, I don't think I have ever seen mine do that when space heating, it only does it when heating DHW.  It is pretty clear to see if you witness it.  you hear the compressor slow and stop, a click and a whirr as the 4 port valve reverses, the compressor starts up this time taking heat from the house and heating up the fins.  It only takes about a minute and as the ice melts you see the cloud of "steam" puff out.  then the compressor stops, the 4 port valve reverses again and it starts up normally again.  It does push up the DHW usage as the COP will be lower, last week when it was less cold we only used 25kWh for DHW

 

What analysis have you had done on your house to predict the actual heating requirements?

I have checked my system and my HW usage is similar to yours. May have to monitor it like @jackhas suggested and see how I get on. I have lowered the stat temp to 20 and see what that does and go from there. May be a month of tweaking here and there. When your heat pump is on what temp does the flow get to Dave? @jackis suggesting lowering the temp for 24 hours and see what that does. The trouble is it is not like a boiler and you see instant results, with our type of house it takes a while for it to respond. The temp does not drop to much over a 24 hour period but one day it may run numerous hours to get it to rise one degree and the next run twice as long to raise it the same amount. My stat has 0.5 degree increments so not precise enough to know what the exact temp is and how far it has risen in a given time.

[jack]

1 hour ago, Pete said:

@jackis suggesting lowering the temp for 24 hours and see what that does. The trouble is it is not like a boiler and you see instant results, with our type of house it takes a while for it to respond. The temp does not drop to much over a 24 hour period but one day it may run numerous hours to get it to rise one degree and the next run twice as long to raise it the same amount. 

 

Not quite: I was wondering about whether running it 24 hours a day - i.e., continuously for days or weeks - at a lower temperature would make much difference to the energy usage you're seeing:

 

4 hours ago, jack said:

I genuinely don't know how different things will be if you just run it 24 hours a day at, say , 28°C versus shortened periods at, say, 35°C.

 

[Pete]

1 hour ago, jack said:

Not quite: I was wondering about whether running it 24 hours a day - i.e., continuously for days or weeks - at a lower temperature would make much difference to the energy usage you're seeing:

 

Thanks, I understood you but explained it wrong