@markc The installers put buffer tanks in to stop low flow errors occurring with their badly designed heating systems. It covers their inadequacies, at your cost.

Mars's system is a bivalent system, therefore he gets paid for the renewable heat he produces ONLY. If his running costs are high due to the poorly designed system, he does not get compensated for this. If it was a stand-alone system, the payment would be deemed, based on the EPC figure.

@markc 

Hi Mark,

I think that you are correct that the DHW valve is not functioning correctly, this is shown by the changes in operation after you lowered the water flow temperature for heating. What appears to be happening now is that the water in your hot water tank is being heated to 50C, at which point the system switches over to heating at 35C. Because the DHW control valve is not closing, water from the ASHP at 35C is still being pumped through the coil in your hot water tank, which of course cools the water in the tank. Since hot water production takes priority over heating, when the water in the tanks falls below the reheat setting the system once more switches over to hot water production at 50C.

First thing to check, there should be a lever on the DHW valve actuator, which can be locked in the open position. Please check by moving the lever backwards and forwards. If the actuator is the type that I think it is, it requires power to open the valve, but the valves closes by spring return when the power is removed. It may be that the actuator has been left in the latched open position.

Please check the above and let me know what you find.

Posted by: @derek-m

@markc 

Hi Mark,

I think that you are correct that the DHW valve is not functioning correctly, this is shown by the changes in operation after you lowered the water flow temperature for heating. What appears to be happening now is that the water in your hot water tank is being heated to 50C, at which point the system switches over to heating at 35C. Because the DHW control valve is not closing, water from the ASHP at 35C is still being pumped through the coil in your hot water tank, which of course cools the water in the tank. Since hot water production takes priority over heating, when the water in the tanks falls below the reheat setting the system once more switches over to hot water production at 50C.

First thing to check, there should be a lever on the DHW valve actuator, which can be locked in the open position. Please check by moving the lever backwards and forwards. If the actuator is the type that I think it is, it requires power to open the valve, but the valves closes by spring return when the power is removed. It may be that the actuator has been left in the latched open position.

Please check the above and let me know what you find.

The lever is loose. i.e. I can movie left to right meaning it is open.

As a test this morning when the DHW was at 35º I turned off the DHW heating, made sure the space heating was on and increased the flow temp to 40º. 2 hours later the DHW is at 40º. So what you have described is definitely happening.

@markc 

Mark,

Move the lever to the valve open position and then let go, it should return to the closed position via spring action. If this is not the case, try holding the lever in the valve closed position and see what affect that  has on your system operation.

You should still get your installer back to resolve the problem and if they try to charge for the visit I would be inclined not to pay since they did not fully complete the installation and commissioning of your system in the first place.

Posted by: @heacol

@markc That valve you have there is a low flow high-temperature valve, you are throttling your system, effectively it cannot breathe. You need to change it to a full bore 3 port valve for it to work properly.

Thanks for your suggestion Brendon. You clearly have a comprehensive understanding of ASHP systems.

I imagine swapping out that valve in isolation would cause other issues due to how my pipework has been designed. 

Posted by: @derek-m

@markc 

Mark,

Move the lever to the valve open position and then let go, it should return to the closed position via spring action. If this is not the case, try holding the lever in the valve closed position and see what affect that  has on your system operation.

You should still get your installer back to resolve the problem and if they try to charge for the visit I would be inclined not to pay since they did not fully complete the installation and commissioning of your system in the first place.

I've just tried that on another valve that controls flow to the radiators and yes manually opening it (move to the left) is quickly followed by an automatic closing (move to the right).

With the DHW valve in question there is no resistance to the lever left or right so it seems to be permanently open. I've put a call in to the installers (voicemail). As I have a maintenance contract with them this will be covered.

Putting that to one side for the moment, with the DHW turned off, can we get back to your thoughts on the system settings?

@markc 

Hi Mark,

It would appear that the valve is the problem, here is a video you may find of interest.

I don't think that it will be possible to utilise weather compensation with your present system because of the location of your controller in the utility room.

To fully utilise weather compensation it would first require the addition of a remote sensor, either hardwired or wireless. If you wish to consider this option then please let me know and I will have a detailed look at the manual to guide you through the process.

@markc I can guaranty that your pipework will be wrong. Installing these valves it is the equivalent of driving your car with a potato up its exhaust pipe, and you are blaming the car for not getting above 20 miles per hour and having horrendous fuel consumption.

@markc 

Mark,

One thing that you could try would be to tap the valve body with a rubber mallet or a block of wood, which may free the valve if it has some dirt stopping if from closing.

Another thing if you feel up to it, would be to switch off the electric supply and remove the cover from the actuator, as shown in the video. Check that the springs are in place and try moving the internal mechanism.

Posted by: @derek-m

@markc 

Mark,

One thing that you could try would be to tap the valve body with a rubber mallet or a block of wood, which may free the valve if it has some dirt stopping if from closing.

Another thing if you feel up to it, would be to switch off the electric supply and remove the cover from the actuator, as shown in the video. Check that the springs are in place and try moving the internal mechanism.

@derek-m

Aha! It seems the motor had gotten jammed. After quick manual turning of the little cog with some pliers the valve seems to open and close as expected.

I've just set the DHW heating back on and watched the motor open (the level becoming loose). I'll give it an hour or so and see if the valve closes.

Thanks Derek.

Back to the weather compensation, yes I am interested in trying this out.

@markc 

Mark,

It is always a good feeling when you solve the problem and fix it yourself.

Once you are certain that the valve problem is resolved, i would suggest that you set your heating water flow temperature to 35C and DHW to 50C again, and monitor your system to see how this affects the COP values. Because of the valve problem, and the original settings by your installer, your system has been operating with a water flow temperature of 50C under all conditions. It will therefore be highly useful to see the different COP values obtained between DHW production and heating. If, as I suspect, it shows quite an improvement in efficiency, it may be cost effective to have the additional equipment installed to provide active weather compensation.

Without wishing to upset 'she who must be obeyed', you could try manually lowering the water flow temperature for heating, to the point where it no longer meets the heat demand. Obviously, because home heating systems respond slowly to changes in temperature, it would be a matter of making a slight adjustment and then waiting several hours to see the effect.

Mark,

A quick question, how did you produce the graphs? Were they derived from your Ecodan controller?