Hi just moved into a Barn which has underfloor heating and 2 Air source heat pumps. We were on the understanding the one ASHP was for the underfloor heating and the other for the domestic hot water. The whole system is operated is Vaillant with 2 panels that show how much each ASHP is drawing each day in KW and then a single digital control panel where you can alter zones and towel radiators etc. The first few weeks seemed ok although I did put up the DHW to 55 degrees as that had been set at 50 degrees and that sorted out the warm showers. But last week we had a problem where after one shower the water was only luke warm. Plumber came out and adjust a few things like turning off the hot water pump as this he said could be pumping water round the whole system (its a 6 bedroom barn over 4000sq ft) but that then meant the hot water tank was getting hotter but we then couldn't get hot water through. So I turned the pump back on which solved getting hot water but then we were back to luke warm water after one shower. So for last few days I've been turning on the immersion heater now and again so this sorts the hot water situation.
My question really relates to the 2 ASHP as we have now been told one operates the DHW and also the underfloor heating needs and the second ASHP will only come on if extra power is needed. From my perspective is this not correct as I would have thought it would have been better to have one ASHP for the underfloor heating initially and the other for DHW and then if the first one for the underfloor heating needed extra (we have around 20 individual zones) then surely this would then draw from the DHW as that pump should not be on that much?
The plant room also seems to be constantly on with the DHW as well, so I'm assuming there must be fault somewhere as if my thinking is correct, the DHW should be stored up to temp and then only cycle is the storage falls below a certain temp.
Assuming it is your property, did the previous owners provide the instructions for it? Any diagrams or schematics you can share? Do you have details of the original installer/heating engineer that you can contact?
Others in the forum have real experience of sizing/adjusting heat pumps, but it may also help to share the model(s) of the heat pumps, year of install if you know it.
Grant Aerona 290 15.5kW, Grant Smart Controller, 2 x 200l cylinders, hot water plate heat exchanger, Single zone open loop system with TRVs for bedrooms & one sunny living room, Weather compensation with set back by room thermostat based load compensation
My question really relates to the 2 ASHP as we have now been told one operates the DHW and also the underfloor heating needs and the second ASHP will only come on if extra power is needed.
This would be most usual normal arrangement for what is called a cascade
Plumber came out and adjust a few things like turning off the hot water pump as this he said could be pumping water round the whole system (its a 6 bedroom barn over 4000sq ft) but that then meant the hot water tank was getting hotter but we then couldn't get hot water through. So I turned the pump back on which solved getting hot water but then we were back to luke warm water after one shower
It could be doing what the plumber says or it could simply be recirculating through the tank. You can tell by how quickly you get hot water at the furthest outlet; when you say 'we then couldn't get hot water through' - how long did you wait? With a big property you are going to wait a long time for water to get to the outlet unless you have recirculation (like hotels do, basically a 2 pipe DHW system where water continually circulates - and of course loses heat!)
The plant room also seems to be constantly on with the DHW as well, so I'm assuming there must be fault somewhere as if my thinking is correct, the DHW should be stored up to temp and then only cycle is the storage falls below a certain temp.
That seems inconsistent with the statement that one ASHP does it all unless its really cold. If this were true then, unless its really cold, there would be no space heating if DHW were on all the time! On the other hand if you do have a recirculating DHW system you will need DHW on continuously unless the recirculation pipes are very well insulated (whats the betting that they arent!) because they will be losing heat all the time. In this case the only way to do things practically would be to have one ASHP dedicated to DHW.
More info needed and we can then talk you through options. You may have to source a diagram. Just to be clear the diagram of interest is a DHW/space heating system diagram - the question is currently not really an ASHP specific question, its a system question which would apply equally whatever the heat source - it might come down to an ashp question later once we understand the system).
This post was modified 3 weeks ago 11 times by JamesPa
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
I did put up the DHW to 55 degrees as that had been set at 50 degrees and that sorted out the warm showers.
That suggests to me that you have loss of heat in the pipework between the DHW tank and the showers.
The temperature of the DHW shouldn't need to be above 45°C.
55°C - 60°C is where the human body's own pain reflex kicks in. If you touch something that hot, your arm muscles should autonomously cause your hand to retract.
As another example, if you were to buy an off-the-shelf anti-scald mixer valve, it would normally be supplied preset to 42°C
You can adjust it higher (& lower) during installation, but that gives you an idea of what's regarded as 'safe and normal'.
Hi just moved into a Barn which has underfloor heating and 2 Air source heat pumps. We were on the understanding the one ASHP was for the underfloor heating and the other for the domestic hot water. The whole system is operated is Vaillant with 2 panels that show how much each ASHP is drawing each day in KW and then a single digital control panel where you can alter zones and towel radiators etc. The first few weeks seemed ok although I did put up the DHW to 55 degrees as that had been set at 50 degrees and that sorted out the warm showers. But last week we had a problem where after one shower the water was only luke warm. Plumber came out and adjust a few things like turning off the hot water pump as this he said could be pumping water round the whole system (its a 6 bedroom barn over 4000sq ft) but that then meant the hot water tank was getting hotter but we then couldn't get hot water through. So I turned the pump back on which solved getting hot water but then we were back to luke warm water after one shower. So for last few days I've been turning on the immersion heater now and again so this sorts the hot water situation.
My question really relates to the 2 ASHP as we have now been told one operates the DHW and also the underfloor heating needs and the second ASHP will only come on if extra power is needed. From my perspective is this not correct as I would have thought it would have been better to have one ASHP for the underfloor heating initially and the other for DHW and then if the first one for the underfloor heating needed extra (we have around 20 individual zones) then surely this would then draw from the DHW as that pump should not be on that much?
The plant room also seems to be constantly on with the DHW as well, so I'm assuming there must be fault somewhere as if my thinking is correct, the DHW should be stored up to temp and then only cycle is the storage falls below a certain temp.
Many thanks
Paul
I have found some schematics and also attached some pics of plant room. Can't find anything regarding the hot water pipe run though
This post was modified 3 weeks ago 2 times by Paullacey
Nice neat plumbing job! I cant see the plant room on the rather low resolution plan. Where is it?
Also the key drawing 12327-1000030975 is too low resolution to read (and rotated through 90 degrees). If you would like to repost in higher resolution and the correct orientation it might be possible to work out. A legible version of 12329-1000030977 would also be good.
This post was modified 3 weeks ago 2 times by JamesPa
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
They are better but still difficult to read. Can you please upload the image files rather than pasting them as images, then they can be downloaded at full resolution and rotated so that they can be read easily. Also where is the plant room on the plan.
These are certainly what's needed to work out what's going on and, as they appear to have been produced by Vaillant, you may also be able to get help from Vaillant if it cant be diagnosed here.
This post was modified 3 weeks ago 3 times by JamesPa
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
the plant room is next to the games room/playroom/gym
Thats a blessing, at least its in the middle. If you can post the files as opposed to pasting the images I will take a look at them, it should be easy to work out, they are exactly what is needed.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
@paullacey From the diagrams I assess you have 2 heat pumps plumbed in "tandem" but controlled in "cascade". What the second heat pump can do is the same as the first one, but only if commanded to (cascade).
Think of a tandem bike with 2 riders. Either rider could provide energy to propel the bike. Now think of a set of instructions; rider one pedals on the flat, rider two must assist only when the speed falls to say, 8 mph.
In this scenario if rider 1 becomes exhausted, rider 2 takes all the strain.
If heat pump one struggles or totally fails in any way the 2nd heat pump can still perform some limited heating.
