So that I can try to create a mental picture of your system, the pump whose speed you have been changing, is it located inside your heat pump or external?
If your system is happy running with a pump speed of 1 and it improves efficiency, then I see no reason to change back, unless you wish to carry out a trial to see if the efficiency again reduces.
It would be useful if you try to draw a schematic of your system. If there are items that you don't recognize then either find the manufacturer's nameplate and Google the model number, or provide a photo and we can see if we can locate the details.
Derek.......sorry for the delay in responding, I have had to wait until i was fit enough to get in the loft!
Regarding pump speeds........I am now running the pump at Speed 1 and cannot see any problems as yet, although I am not entirely sure which pump I am controlling. The service menu on the FTC only references the one pump but there are three in the system all part of the packaged ecodan cylinder.
The one on the space heating is the AUTO pump so would imagine its not that one so assume it is the pump on the Primary Heat pump circuit?
The other pump which is on the DHW circuit is puzzling because that seems to be running continuously and quite hot, surely this only needs to run when the DHW is calling for heat??
As requested Derek I have attached a schematic, have highlighted a couple of anomalies, the expansion vessel is shown on the flow but is actually on the return, however have googled the the manufacturers info and they state it should be on the return.
The flow & return sensors are mounted very loosely in a copper "U" trough pasted to the pipes and were not insulated.
Just a recap on the initial post which was low COP.....I think we have established between us that Melcloud is reporting false energy data (Strangely it has not reported any usage for Saturday but Sundays is double) and that as I am getting a smart meter reading at the moment during this last weeks cold snap of around £9 to £10-00 for an all electric house and we are keeping all rooms at an average of 20C that the unit can't be consuming more than about 25/30KWh its efficiency must be reasonable?????.
After getting the WC Curve what seems reasonably tuned I have reverted back to Auto Adapt with TRV's controlling 3 rooms that are little used and don't seem to be having any cycling issues (I think) but more economic than WC
Would really welcome anybody's explanation of why the DHW is running when no call for heat.?
Plate loading the DHW coil, that’s a new one on me…. And is madness. Totally unnecessary and a massive performance hog.
Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.
My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.
@HughF, sorry I didn't understand what you mean about plate loading?
It is the plate heat exchanger (PHE) which is item 12 in your schematic. I can only assume that your installer has used one because it would appear the your hot water cylinder does not contain a heating coil. If it is piped up as shown in the schematic, then it would appear to be incorrect. The warm water from your heat pump is shown going into the PHE at the top left-hand corner, with the cooler return water coming out at the bottom left hand corner. On the secondary side of the PHE, the DHW is shown being drawn from the bottom area of the hot water cylinder and going into the top right-hand corner of the PHE, with the warmed DHW coming out of the bottom right-hand section of the PHE. This warmed water then goes via the Scale Trap (13) and the DHW Circulating Pump (14) back to the hot water cylinder.
Whilst it will still work if the water flow through both sides of the PHE is in the same direction, it is actually designed for contraflow operation, which is more efficient. I would suggest that you check if the PHE is piped up as shown in the schematic and Google the make and model to confirm how it should be connected.
The flow & return sensors are mounted very loosely in a copper "U" trough pasted to the pipes and were not insulated.
Where in your circuit are the Primary flow and Primary return thermistors mounted? (Also called LWT and RWT) Also have you managed to get differential readings across your central heating flow and returns where the CH flow exits the low loss headder and where the CH return enters the headder tank? See marked up schematic I’ve indicated where these might be read.
We are currently reviewing the usefulness or otherwise of the low loss headder in our system as the DT is very small. 3c compared to 7c on the Primaries. We have also slowed pump speed to 13ltrs.
@derek-m I had missed that the dhw tank didn’t have a coil in it, silly me. That would indeed require an external heat exchanger to load up the cylinder. Quite a nice solution actually, although it requires another pump, that has to be a bronze headed one, to circulate the dhw through the plate. And makes for a more complex control strategy.
it must be an ancient install because heat pump rated unvented cylinders are easily had off the shelf from all the merchants.
Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.
My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.
@HughF, sorry I didn't understand what you mean about plate loading?
It is the plate heat exchanger (PHE) which is item 12 in your schematic. I can only assume that your installer has used one because it would appear the your hot water cylinder does not contain a heating coil. If it is piped up as shown in the schematic, then it would appear to be incorrect. The warm water from your heat pump is shown going into the PHE at the top left-hand corner, with the cooler return water coming out at the bottom left hand corner. On the secondary side of the PHE, the DHW is shown being drawn from the bottom area of the hot water cylinder and going into the top right-hand corner of the PHE, with the warmed DHW coming out of the bottom right-hand section of the PHE. This warmed water then goes via the Scale Trap (13) and the DHW Circulating Pump (14) back to the hot water cylinder.
Whilst it will still work if the water flow through both sides of the PHE is in the same direction, it is actually designed for contraflow operation, which is more efficient. I would suggest that you check if the PHE is piped up as shown in the schematic and Google the make and model to confirm how it should be connected.
@HughF - The cylinder is a pre-plumbed Ecodan Unit and have had a look at the catalogue and this is how it is factory set.?
The flow & return sensors are mounted very loosely in a copper "U" trough pasted to the pipes and were not insulated.
Where in your circuit are the Primary flow and Primary return thermistors mounted? (Also called LWT and RWT) Also have you managed to get differential readings across your central heating flow and returns where the CH flow exits the low loss headder and where the CH return enters the headder tank? See marked up schematic I’ve indicated where these might be read.
We are currently reviewing the usefulness or otherwise of the low loss headder in our system as the DT is very small. 3c compared to 7c on the Primaries. We have also slowed pump speed to 13ltrs.
-- Attachment is not available --
I have attached cylinder drawing showing where the sensors are mounted
Regarding temperatures I currently don't have anything to accurately measure (Can you recommend anything for occasional use, my cheap clamp on's are very poorly calibrated).
My DT is generally 2-3c and I am running the pump at 1 giving around 11 ltrs/min.
Derek.......sorry for the delay in responding, I have had to wait until i was fit enough to get in the loft!
Regarding pump speeds........I am now running the pump at Speed 1 and cannot see any problems as yet, although I am not entirely sure which pump I am controlling. The service menu on the FTC only references the one pump but there are three in the system all part of the packaged ecodan cylinder.
The one on the space heating is the AUTO pump so would imagine its not that one so assume it is the pump on the Primary Heat pump circuit?
The other pump which is on the DHW circuit is puzzling because that seems to be running continuously and quite hot, surely this only needs to run when the DHW is calling for heat??
As requested Derek I have attached a schematic, have highlighted a couple of anomalies, the expansion vessel is shown on the flow but is actually on the return, however have googled the the manufacturers info and they state it should be on the return.
The flow & return sensors are mounted very loosely in a copper "U" trough pasted to the pipes and were not insulated.
Just a recap on the initial post which was low COP.....I think we have established between us that Melcloud is reporting false energy data (Strangely it has not reported any usage for Saturday but Sundays is double) and that as I am getting a smart meter reading at the moment during this last weeks cold snap of around £9 to £10-00 for an all electric house and we are keeping all rooms at an average of 20C that the unit can't be consuming more than about 25/30KWh its efficiency must be reasonable?????.
After getting the WC Curve what seems reasonably tuned I have reverted back to Auto Adapt with TRV's controlling 3 rooms that are little used and don't seem to be having any cycling issues (I think) but more economic than WC
Would really welcome anybody's explanation of why the DHW is running when no call for heat.?
Derek.......sorry for the delay in responding, I have had to wait until i was fit enough to get in the loft!
Regarding pump speeds........I am now running the pump at Speed 1 and cannot see any problems as yet, although I am not entirely sure which pump I am controlling. The service menu on the FTC only references the one pump but there are three in the system all part of the packaged ecodan cylinder.
The one on the space heating is the AUTO pump so would imagine its not that one so assume it is the pump on the Primary Heat pump circuit?
The other pump which is on the DHW circuit is puzzling because that seems to be running continuously and quite hot, surely this only needs to run when the DHW is calling for heat??
As requested Derek I have attached a schematic, have highlighted a couple of anomalies, the expansion vessel is shown on the flow but is actually on the return, however have googled the the manufacturers info and they state it should be on the return.
The flow & return sensors are mounted very loosely in a copper "U" trough pasted to the pipes and were not insulated.
Just a recap on the initial post which was low COP.....I think we have established between us that Melcloud is reporting false energy data (Strangely it has not reported any usage for Saturday but Sundays is double) and that as I am getting a smart meter reading at the moment during this last weeks cold snap of around £9 to £10-00 for an all electric house and we are keeping all rooms at an average of 20C that the unit can't be consuming more than about 25/30KWh its efficiency must be reasonable?????.
After getting the WC Curve what seems reasonably tuned I have reverted back to Auto Adapt with TRV's controlling 3 rooms that are little used and don't seem to be having any cycling issues (I think) but more economic than WC
Would really welcome anybody's explanation of why the DHW is running when no call for heat.?
Hi Derek...........Did you have any ideas on the DHW Pump running when not calling for heat?
Hi Dave,
I was under the impression that the Ecodan has a water pump that is internal to the heat pump unit, and this is the one whose speed is being controlled. You may have to check your particular model, since you appear to have an external pump in the return pipework.
Water pumps that have speed control would normally have two cables connected, one to supply power and the other being the speed control signal.
My assumption would be that the DHW Circulating Pump would only need to run when the system is heating the DHW via the PHE, otherwise it could have a cooling effect on the water in the cylinder besides wasting electricity.
Are you sure the DHW pump is over-running? It would quickly be pumping the cold water that was entering the cylinder low down as hot water was drawn off up into the hotter water above and you would have a tepid tankful in short order. Is it the fact that it is hot that makes you think this? I find the cylinder side loop of the PHE gets hot and remains very warm even several hours after the HW cycle has run – a lumpy run of metallic bends, valves and the pump itself all just leaking heat out of the cylinder! I think it is too hot all the way down this loop just to be the copper conducting heat, there must be a continuous slow circulation of water cooling in the pipework and flowing down into the bottom of the tank. I was disappointed by the apparent heat loss of the cylinder after installation – I think I have partly improved it by painstakingly insulating the pipework. My installers insulated most of straighter pipes leading up to the cylinder (though not well enough for my liking) but left bare the mess of copper that comes attached to the front of the packaged unit. I have managed to closely insulate a lot of it but circular pump housings just have a loose blanket of rockwool-type stuff.
I think the cylinder pipework is a compromised design as it has been laid out for compactness but at the expense of some practicality. The clips for the thermistors, the return in particular, are on pipes that are awkward to access and insulate properly. Given that accurate temperatures are required for the FTC to do its job most effectively I would have thought proper pockets should have been provided.
Mitsubishi EcoDan 8.5 kW ASHP - radiators on a single loop 210l Mitsubishi solar tank Solar thermal 3.94kW of PV
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