Posted by: @enc

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@kev-m seems like its vintage then! Would there be any benefit to updating the controller other than for ease of control or smarter data tracking?

 

Really hoping to start to see some improvements now. I think I am understanding what you are saying that we want to temperature compensation curve to do all the work based on outside temperature, and not the room thermostat turning it on and off. To figure out the temperature compensation curve initially we need to have a play around adjusting this without the room themostat interfering i.e. have stat on 30, so high when we do this? However, once we have the curve right we can adjust the stat back down to something more like 21 degrees?

 

This brings me onto my next question of radiators! We have three floors and 11 rads throughout the house, plus 3 towel rails. As it gets hot at the top of the house the bedrooms are quite uncomfortably hot at night, does it make sense to have these rads on 1 or 2 at all times and then the ones on the ground floor at a higher setting i.e 5? Or do we want them all on high and this heat at night time is due to the temperature compensation curve being too high at low temperatures?

 

Thanks again for all your help. You probably have to go through this whole conversation so many time with newbies to ASHPs!

I can't beat @Derek-m's explanation so I won't try.  And @HughF's advice about the TRVs.  I don't know if the newer controllers will work with your ASHP and to be honest, I don't think you'd gain a lot anyway. 

I'd be interested to know if the lower temps keep the house warm enough. 

@derek-m Thank you so much Derek that is so helpful. First step to order some thermometers and get the data collecting :D!

Although I keep coming up with more questions the more I think about this! Hopefully these will be the last ones for a while ...

1. Is there a water temperature that is too low? Or is it literally the lowest water temperature that keeps your home warm at a constant temperature will do it?

2. What do the values for the outside temperatures set on the weather compensation actually mean? If at the moment the setting is -2 for the lower and 15 for the higher value, if the temperature outside is outside of these ranges will the heat water at the higher and lower temperatures that have been set? So in my case 30 degrees and 40 degrees?

3. What happens in summer if my thermostat is at 25 degrees and it never reaches that indoors, will the heat pump continually be circulating water at 30 degrees around the house? This seems like a bit of a waste.

We are finding its actually a bit hot inside our house now despite having reduced the water flow temperatures significantly. 

Thanks again!

@kev-m currently the lower temps are keeping it too warm (based on my comfort rather than any readings). However, yesterdays usage was 23.2kwh for the day despite having the heating on constantly. So it is matching what we were using with it just being on whilst my husband was working at home. In that respect it is looking positive that we can have a constant temperature 24/7 for the same usage, and I am sure we will be able to further optimise going forwards. Will keep you all posted :).

@enc you've got a couple of options. You can lower the temps, or push out the lower boundary e.g. from -3 to -5. You're then just lengthening the slope. I'd just keep adjusting slowly down by a couple of degrees every few days until you get to what you feel is comfortable. Then you are basically done. It'll cost you less money and the whole house will feel warmer more of the time - winning all round.

@enc to answer your questions

1. Most ASHP have a minimum flow temperature - just keep going down and eventually it'll stop letting you adjust. Its probably something like 20 or 25 degrees
2. The settings are simple, your heat pump will heat the rads to 40 degrees when its -2 and when its 15 degrees the maximum will be 30. It makes a slope between the two and adjusts automatically e.g. at twenty degrees it'll be something like 33 degrees at the rads.
3. In the summer it shouldn't be on, but you can always just turn down the stat to something like 18. This is the issue running on the Stat and not the actual controller. I just lower mine so it never kicks on.

Posted by: @enc

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@derek-m Thank you so much Derek that is so helpful. First step to order some thermometers and get the data collecting :D!

 

Although I keep coming up with more questions the more I think about this! Hopefully these will be the last ones for a while ...

1. Is there a water temperature that is too low? Or is it literally the lowest water temperature that keeps your home warm at a constant temperature will do it?

2. What do the values for the outside temperatures set on the weather compensation actually mean? If at the moment the setting is -2 for the lower and 15 for the higher value, if the temperature outside is outside of these ranges will the heat water at the higher and lower temperatures that have been set? So in my case 30 degrees and 40 degrees?

3. What happens in summer if my thermostat is at 25 degrees and it never reaches that indoors, will the heat pump continually be circulating water at 30 degrees around the house? This seems like a bit of a waste.

 

We are finding its actually a bit hot inside our house now despite having reduced the water flow temperatures significantly. 

 

Thanks again!

Hi Emma,

Don't worry about asking questions, it what we are here for. It also helps keep me out of mischief. 😋 

1) For the heat pump to operate, it normally requires a LWT that is at least 5C above the desired indoor temperature. Because your heat pump is an older model I cannot be 100% certain, but I believe that most, if not all, the more modern heat pumps operate in the following manner.

When operating in WC mode, the required LWT is set by the controller in conjunction with the ambient air temperature measurement. So with your present WC curve the LWT at 10C ambient should be approximately 33C. This should be the temperature of the water going from the heat pump to the radiators. As the water flows through the radiators it gives up heat energy and cools, so that the RWT going back to the heat pump is lower than the LWT by a factor that is referred to as the DeltaT. The DeltaT in a heat pump system is normally in the region of 5C, so in the above case you should expect 33C water going to the radiators and 28C water coming back. The rate at which heat energy is transferred from the water to the radiator, and hence to the surrounding air, is dependent upon the DeltaT between the water temperature and the surrounding air temperature, the higher the water temperature, the greater the heat transfer rate. It is also not linear, but follows and exponential curve.

The quantity of heat energy transferred from the heat pump to the radiators is dependent upon the DeltaT between LWT and RWT and the flow rate, normally measured in litres per minute. In the above example, say your heat pump is producing water at a LWT of 33C and at a flow rate of 25l/min, with a RWT of 28C, then the system is in balance. If the indoor temperature now starts to increase, the radiators will not absorb as much heat energy from the water and the RWT will start to increase. The controller senses the increase in RWT and lowers the flow rate to say 20l/min, thereby reducing the amount of heat energy being transferred, and the RWT reduces to 28C once more. The controller is continually monitoring the temperatures and flow rate and making adjustments.

As the indoor air temperature increases, the speed of the internal water pump, and hence flow rate, will be reduced to maintain balance. But just as your car engine has a minimum speed, so does the water pump. If, with the water pump at minimum speed the RWT continues to increase it will reach a point where the controller will stop the compressor, to stop heating the water.

I would say that the minimum setting for LWT within the WC curve would be 25C.

2) The setting of the WC curve is required to match the output energy produced by the heat pump to the heat loss of your home. As the ambient air temperature falls, the DeltaT between the indoor air and the outdoor air increases, and so does the heat loss. To keep the indoor air temperature reasonably constant, the heat pump needs to produce more heat energy.

The -2C and 15C used in your present WC curve are just chosen reference points, you could just as easily have used -10C and 20C.

The more important values are the setting of the required LWT at the chosen reference points. In your present case you are requesting a LWT of 30C when the ambient air temperature is 15C, and a LWT of 40C when the ambient air temperature is -2C. These values define the slope of the WC curve.

I would suspect that as the ambient air temperature increase above 15C, then the LWT will be held at 30C. The same should happen at the lower ambient air temperature.

The objective is to match the slope of the WC curve to the heat loss characteristics of your home. As a starting point I often suggest a LWT of 25C at and ambient of 20C, and a LWT of 50C at an ambient of -5C. The 25C at 20C should not be too far from correct, so if you find that at an ambient of 10C the indoor temperature is too high, then lower the 50C at -5C to say 45C at -5C.

3) Unless you have a solar PV or solar thermal system, you will still require your heat pump to run for hot water during the Summer. To ensure that the heating does not run then just turn down the thermostat.

I hope that this answer your questions, but please feel free to ask more. You are also helping other readers who are too shy to ask.

@derek-m Thank you so much for the detailed guidance in response to my questions :), and sorry for my silence over the weekend.... busy doing diy fitted wardrobes 🤣 so wasn't online much! Looking forward to being able to apply this to my system when I get some better data.

Still waiting to get thermometers, and in the meantime I just lowered the upper value to something like 34 degrees at -5, and the house seems to be warm enough and consistent ish... however, I am still trying to figure out how to get the ground floor to be warm enough without boiling us as you go up the levels. 

To your question on the radiator balancing, no I don't think they have been. I had also assumed that the top of the house was warmer because of the hot air rising, however now thinking about it the water tank is at the top of the house. Does this mean that they are the rads that receive the flow of water first? I have turned down the flow temperature of the water really low, but actually would it work better say to have a slightly higher water temp but have those radiators at the top of the house that are close to the water tank down really low say 1 or 2 on the dials, then on the middle floor 3 and up to 4/5 on the ground floor furthest away? That way if it is the case that the rads at the bottom receive water flow last the water will be hotter when it reaches them without having wasted it at the already hot top of the house.

Is balancing the radiators something I can do myself? I only know I have 1-5 dials on the right hand side as I look at the rads and that water goes in one side and out the other, and that is the extent of my knowledge.

Posted by: @enc

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@derek-m Thank you so much for the detailed guidance in response to my questions :), and sorry for my silence over the weekend.... busy doing diy fitted wardrobes 🤣 so wasn't online much! Looking forward to being able to apply this to my system when I get some better data.

Still waiting to get thermometers, and in the meantime I just lowered the upper value to something like 34 degrees at -5, and the house seems to be warm enough and consistent ish... however, I am still trying to figure out how to get the ground floor to be warm enough without boiling us as you go up the levels. 

To your question on the radiator balancing, no I don't think they have been. I had also assumed that the top of the house was warmer because of the hot air rising, however now thinking about it the water tank is at the top of the house. Does this mean that they are the rads that receive the flow of water first? I have turned down the flow temperature of the water really low, but actually would it work better say to have a slightly higher water temp but have those radiators at the top of the house that are close to the water tank down really low say 1 or 2 on the dials, then on the middle floor 3 and up to 4/5 on the ground floor furthest away? That way if it is the case that the rads at the bottom receive water flow last the water will be hotter when it reaches them without having wasted it at the already hot top of the house.

Is balancing the radiators something I can do myself? I only know I have 1-5 dials on the right hand side as I look at the rads and that water goes in one side and out the other, and that is the extent of my knowledge.

Because water will take the route of least resistance, if the water pump is on the ground floor, the water would prefer to flow to the radiators on the ground floor, rather than 'climbing' the stairs to an upstairs floor. It will also prefer to flow through the first radiator on the loop, rather than 'trailing' down the pipe to find another radiator, even if it is more 'attractive'. 😎 

So to encourage the water to 'feed' all the radiators, including the 'runt' at the end, the system needs to be balanced.

At one end of a radiator will be the TRV, if fitted, at the other end will be the lockshield valve.

Balancing the system, particularly over three floors, is not a 5 minute job, since it involves opening all the lockshield valves and TRV's fully, and then finding the radiator that is receiving the most heat energy. The lockshield valve is then closed in (but not fully closed) on this radiator, to encourage more of the flow to go to the other radiators. This process is repeated on the next warmest radiator, until you arrive at the 'runt' at the end. It may be necessary to go round again and make further adjustments.

I feel certain you will be able to find YouTube videos that can explain the process much better than me.

When balancing has been achieve, then use the TRV's in the bedrooms and unused rooms to set a lower temperature if required, but leave the TRV's in the most often used rooms fully open, and adjust the WC curve to achieve the desired temperature.

@derek-m I have been fiddling around trying to balance the rads. The lockshield valves were fully open on all of them, but in all honesty I think my attempts at balancing have just caused the rads at the top of the house to not get as much heat (when trvs are fully open on all radiators) rather than encouraging the ones down the bottom to get hotter. I think this is possibly because they were already all getting the same amount of heat, but I think the heat loss at the bottom of the house is greater with it being lower and we have a cat flap which probably doesnt help keep the heat in. 

I am going to keep trying but is there any harm in them all being open if they are heating evenly like this?

I have another new question too. Do you know what the temperature offset on the heating controller is for? It is currently set to 5 degrees but unsure of what this is doing or achieving. Usage is still about 24 kwh per day whatever I seem to do :).

Thanks,

Emma

My radiators also seem to be getting warm and then near cooling down repeatedly throughout the day. Is this normal?

@enc that shows your system is getting your room to temp and then turning off. A defrost cycle should be quick and your rads shouldn't really cool down too much. You might want to try reducing the flow temps again?

@batalto thank you! I will look into that. I had increased it again because the kitchen and hallway downstairs are so blooming cold. Think I am going to have to resort to using the TRVs to control upstairs if I can't figure it out :(. How does my pump know what the room temperatures are by the way? haha