@jamespa yeah, I agreed. My son’s bedroom is on the ground floor with his sisters room above. I need to keep his room all night to over 20 so the fabric of that part of the hose stays high and heats the rooms above.
but very first world issues. I’d like the option to run the main part of the house bit cooler, but I’d done with fiddling for another year. It’s working pretty good now. If I can hold it through heavy defrost conditions next winter, then I’ll stand down….
but, I’ve had work out the control mechanism and balance 5 pumps, 18 UFh loops and 6 rads myself. The 9 zone, 9 stats, closed loop system it was commissioned at did not work. There is no way a typical punter would have got here. If the industry is serious about mass roll out, I’m dubious.
but, I’ve had work out the control mechanism and balance 5 pumps, 18 UFh loops and 6 rads myself. The 9 zone, 9 stats, closed loop system it was commissioned at did not work.
I have yet to hear of a system that actually did work efficiently post installer commission. In fact I cant see how it can - no installer is going to spend the several days of elapsed time required to get WC curve and emitter balance right, and installations occur outside the heating season.
The best we can currently expect in practice is that the system heats and is tolerably efficient, but realistically nothing more. Unfortunately there appears to be a conspiracy of silence over this problem. However this is nothing new. Most, if not almost all, condensing boilers installed since they became mandatory appear to be set up so they dont condense or rarely condense. The fact the UK didnt mandate weather compensation in the UK and operate typically at ~FT75 pretty much guarantees this. So we have all been paying perhaps 10% more for our gas heating than we needed to. Plus ça change
If the industry is serious about mass roll out, I’m dubious.
Personally I don't believe it is. Much easier to do a small number of high price jobs than a large number of low price ones. BG and Octopus may be different however.
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.
yeah, i agree. The time required to fine tune a system is not economical. I absolutely understand why heat pump companies oversize, stat control and get out of town. It breaks down, as mine did, when it did not heat the house. I think if I’d have had the 14kw unit, and I consolidated a few of the zones that I initially did, it would have powered through the problems and “worked”. So in a way, I think I’ll come out of this is a better place.
If you have any form of system separation its not inconceivable that you have a similar or related problem. Just saying but please accept my apologies if you have already been through all of this.
Hi James, we do have separation by the very small pipe I have placed pictures of before on the preplumbed cylinder that has no appreciable volume.
All I know is that if everything is open on the secondary side and its low single figures outside and my flow is set to 45C the heat pump can't get there, compressor will be at 100Hz and the flow temp will get to 42C the return is at 32C and it just stays there till it defrosts so the heat is going into the house and the house temp is stable, hence, my conclusion that its just the heat pump that is undersized.
I could pay have it all replumbed to be completely open loop, but I think I saw someone get urban plumber do that for a Mitsubishi system and it made absolutely no difference to performance.
If you have any form of system separation its not inconceivable that you have a similar or related problem. Just saying but please accept my apologies if you have already been through all of this.
Hi James, we do have separation by the very small pipe I have placed pictures of before on the preplumbed cylinder that has no appreciable volume.
All I know is that if everything is open on the secondary side and its low single figures outside and my flow is set to 45C the heat pump can't get there, compressor will be at 100Hz and the flow temp will get to 42C the return is at 32C and it just stays there till it defrosts so the heat is going into the house and the house temp is stable, hence, my conclusion that its just the heat pump that is undersized.
I could pay have it all replumbed to be completely open loop, but I think I saw someone get urban plumber do that for a Mitsubishi system and it made absolutely no difference to performance.
All noted.
it was @bobtskutter that finally diagnosed the problem (which related to mismatch of pump speed causing throttling at the system separation point) with the @cathoderay installation. Maybe if you post some flow rates, temperatures etc either side of the 'very small pipe' (a low loss header I suspect) he or someone else may be able to rule it out/in.
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.
@gary I'll try and help, but at the moment I'm not really sure what the problem is.
<rant>
On a more general note, I read threads like this and see lots of references to buffers, low loss headers, volumisers and system separation. Please can I make some observations?
A low loss header is a form of HYDRAULIC separation. It allows the heat source (heat pump, gas boiler, stove etc) to have a different water flow rate than the heat emitters (rads, underfloor, fan coil etc). That's it. That is the purpose of a low loss header.
The down side of a low loss header is that it can mix the return water from the rads with the hot water from the Heatpump. This lowers the temperature of the rads and people then say "a low loss header is inefficient". It is not. The thermodynamics still work. The problem is that the rads aren't big enough. To counter act this, people then increase the flow temperature from the Heatpump to increase the blended flow temperature to the rads, which uses more electricity. I am specifically ignoring defrost cycles for now.
System separation is when you install something to prevent the water in the Heatpump from mixing with the water in the rads, i.e. a plate heat exchanger. A plate heat exchanger requires a temperature difference between the hot water (from the heat pump) and cold water (in the rads) to allow energy to transfer. This means the temperature in the water to the rads is lower than the heatpump, if your rads are too small you wont get enough heat out of the system. However, plate exchangers can all so "run out of differential temperature" which is what happens when the temperature to the rads is the same as the flow from the heatpump. This is what was happening with @CathodeRays system. Increasing the flow rate to the rads (by opening all the valves) reduced the temperature leaving the plate exchanger and allowed more energy to be transferred. It's a strange concept, increase the flow which lowers the temperature, which allows more energy transfer which then increases the temperature of the room because the rads are working properly. I'm still ignoring defrost cycles!
A buffer and volumiser are roughly the same thing. (Please don't start yelling at me just yet 😉 ) They both contain a volume of water that allows the SYSTEM to maintain a constant temperature. The big difference between them is a buffer is a form of hydraulic separation and has all the "problems" of a low loss header. A volumiser is just a way of adding more water to the system, it does not provide hydraulic separation. In theory, buffers and volumisers can help with defrost cycles where the heat pump is putting cold water into the system. In theory a buffer can prevent the cold water getting to the rads, and placement of volumiser on the outlet side of a heat pump can do the same thing. The problem is all the buffers and volumisers I read about MIX the flow in and the flow out. If the buffer or volumiser had thermal statification systems inside it then it could cope with a sudden slug of cold water without causing the outlet temperature to drop.
As an example, heat up your hot water cylinder. Then turn on a hot tap SLOWLY. You will notice the bottom of the tank goes cold but the top of the tank stays hot. This is thermal statification. If the velocity of cold water going into the buffer or volumiser is too big it will mix up the stored water and cause the temperature to drop. The only buffer vessels I've seen with thermal stratification systems are very very large commercial storage systems, and mixergy hot water tanks. If the buffer vessel or volumiser was stratified, the cold water in the bottom of the vessel would slowly blend with the hot water and the system temperature would remain reasonably constant. If using a buffer vessel, it would need very careful design to ensure the cold water didn't recycle back to the heatpump during the defrost, otherwise it might stop the heatpump defrosting.
</rant> 🙂
I have no affiliation with mixergy. I'm a Chemical Engineer.
@bobtskutter - you are welcome to rant. You are able to express yourself (and complex ideas) very well, and your posts are valuable contributions to the forum.
Midea 14kW (for now...) ASHP heating both building and DHW
This is the 'LLH' on the preplumbed cylinder to separate the primary and secondary sides. (this isn't my tank).
Flow rates on the primary side are 15L/min which is the recommended flow for the heat pump. On the secondary side there are 2 zones and associated secondary pumps for rads and UFH. No way of knowing the flow rates on the secondary have the 1,2,3 options on the pumps.
The issue is that the heat pump cannot get to the set flow temperature during the coldest periods similar to @davidnolan22 experience from what I have read.
Here is a plot from early Feb I have chosen a day when defrosts weren't compounding the issue. Heating starts at 01.00 it took 2 hours for the heat pump to reach the set flow temp of 45C. The return temp is 10C lower than the flow. When there are defrosts hourly then it will never reach the set flow temp.
This isn't because the house was cold the heating was running all day and only stopped at 23.30 to run the DHW for 90 mins prior to return to heating.
This is the reason I believe the heat pump is undersized.
If there are experiments I can do with the pump speeds happy to do that.
This is the 'LLH' on the preplumbed cylinder to separate the primary and secondary sides. (this isn't my tank).
Flow rates on the primary side are 15L/min which is the recommended flow for the heat pump. On the secondary side there are 2 zones and associated secondary pumps for rads and UFH. No way of knowing the flow rates on the secondary have the 1,2,3 options on the pumps.
The issue is that the heat pump cannot get to the set flow temperature during the coldest periods similar to @davidnolan22 experience from what I have read.
Here is a plot from early Feb I have chosen a day when defrosts weren't compounding the issue. Heating starts at 01.00 it took 2 hours for the heat pump to reach the set flow temp of 45C. The return temp is 10C lower than the flow. When there are defrosts hourly then it will never reach the set flow temp.
This isn't because the house was cold the heating was running all day and only stopped at 23.30 to run the DHW for 90 mins prior to return to heating.
This is the reason I believe the heat pump is undersized.
If there are experiments I can do with the pump speeds happy to do that.
Looking at the plot it looks like the compressor frequency (yellow line) is zero from about 0L00 to 19:00. Am I misreading?
2 Hours to get up to temperature is not really a surprise (my house takes over 24hours to get up to temperature), particularly with UFH if the slab has been allowed to cool. Have you go a plot when defrost is compounding the issue.
This post was modified 6 hours 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.
2 Hours to get up to temperature is not really a surprise (my house takes over 24hours to get up to temperature)
The house is up to temperature the floor won't be cold it was running for hours before DHW at 35C, just trying to maintain it/batch heat during the coldest times overnight.
@davidnolan22 The UFH is retrofit so its only 20mm thick 150mm centres about 90sqm and then 8 rads upstairs.
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