1-The primary pump is already set to max speed (5), so I have to look to reducing the secondary circulation pump speed. I haven't found a way, yet, of doing so with the installed Grundfos UPM2 and may have to consider replacing the pump.
2- I am using weather compensation, but as mentioned, the temperatures given were whilst we are having a rather mild spell.
Turning to James's points, I don't feel that I could commit to the extensive changes suggested and it would no be possible to find a contractor here in the Algarve to do the work, so I have to do the best I can, with what I have.
May I ask James two questions, i.e.
In your view, am I wasting my time in trying to find a way to vary (and potentially reduce) the secondary pump speed?
Assuming I could vary the speed of the secondary pump, what flow and return temperature differentials at the buffer tank might be reasonable? (I would hope to test with colder ambients than the 14C today)
Happy New Year to All
Converting your system by changing the function from a buffer tank to a volumiser is not such a major task, that any competent plumber should be able to perform with ease.
The process should consist of the following modifications :-
1) Disconnect the two 'flow' pipes from the top section of the buffer tank
2) Connect the disconnected pipes using a suitable length of pipework.
3) Remove the secondary water pump and connect the inlet and outlet pipes with a new section of pipe.
4) Disconnect the return pipe from the heat emitters at the lower section of the buffer tank, and connect, using suitable pipework, into one of the now empty ports at the upper section of the buffer tank.
5) Plug the two buffer tank ports that no longer have pipework connected.
The water from the heat pump should now flow directly to the heat emitters, with the return water flowing through the buffer tank, from top to bottom. The buffer tank is now a volumiser.
Converting your system by changing the function from a buffer tank to a volumiser is not such a major task, that any competent plumber should be able to perform with ease.
Agreed.
With two or three isolating valves it can even be done reversibly. Basically bypass the buffer tank on the flow, bypass the secondary pump, fitting valves so you can select either route.
I am very grateful to JamesPa for his very interesting explanation and for the subsequent comments by both James and Derek.
I don't want to tackle the job at the start of winter and I have a very poor opinion of plumbers/ heat engineers here in the Algarve so I will continue to explore the secondary pump speed control at this time. I will attach a photo of my setup although this does not show the large DHW tank that was more recently added.
Having recently uninstalled a solar water heater from my roof terrace, I have two contractors visiting next week to quote for a 16-18 Solar PV, but I will be more careful with this than I was able to be when buying the Mitsu before the gas tank ran out!
One possible way to reduce the flow rate in the secondary circuit would be to throttle in one of the isolation valves, preferably one after the secondary water pump.
It merely means that the flowrates in the primary and secondary circuits can be different.
it actually says 'unconnected' which, I fear, is indeed what it means. As we all know for a buffer to work efficiently the flow rates in the circuits need to be in a correct relationship. So while they may not be the same they definitely have to be 'connected' if the buffer is not to cost 10-15% in efficiency.
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.
Hell Mars - good of you to check up and I am afraid that I have not yet modified the buffer tank function.
I have been preoccupied with installation of a 12 panel solar system and trying to optimise the use of this together with the ASHP on summer duties, i.e. just producing DHW. I am in Portugal and the contractor who did the DHW tank and the solar, disappeared on holiday after completing the solar.
I have still have some questions for him about the solar, but I want to follow up with a request that he changes the buffer tank configuration. However, he is a "non- believer" and I may have some difficulties with him.
I also wanted to have better monitoring facilities for a before and after comparison but I have got stuck on that also. The comprehensive systems you have in UK are not available here in Portugal and in any case, at my age, I could not justify that sort of expenditure just for short term set up.
I have a DIN rail Zigbee energy measurement unit ready to install and some simple temperature measurement devices, but lots of other things needing attention and I am slow now.
One other aspect which suffered after the ground floor DHW tank installation was the long delay getting water, particularly to kitchen and distant bathroom so looking for solutions to that. (Upside down house!)
I am seeking help from JamesPA; Derek M; Mars and anyone else who can contribute on the topic of re-purposing a buffer tank as previously discussed!
I have just had a lengthy session with the Portuguese contractor who installed the DHW extension to my Mitsubishi ASHP, with regard to changing the function of the buffer tank to become a volumiser.
I have much more respect for him than I have for the original installer of the ASHP, but I have, so far, failed to convince him that it is appropriate to make this change. It was difficult for me to get over the problem of balancing primary and secondary flows, especially with an unsuitable "dumb" pump.
Beyond that, his concern is that whilst the secondary pump is apparently capable of dealing with the pipe friction etc. in the radiator system, he has no confidence that the pump in the Mitsubishi equipment can deal with it in the same way. (In retrospect, I think it highly unlikely that the original installer of the ASHP checked the flow and pipe resistance in the radiator system).
My contractor made the point that the pumps in Daikin ASHP's (that he is more familiar with) would certainly not cope.
Again my ASHP is a PUHZ-SW120YHA with an EHSC-VM20D.Uk Hydrobox
I would appreciate any comments which might reassure me and ultimately, my contractor
First to make the buffer to a volumiser, you need to compare the secondary to pump capacity and head curve. This should be easy enough for the plumber. The primary pump curve will be in the heat pump install manual. Your secondary will be available within the paperwork that came with the pump or online.
The de-risked version is to convert from 4 port buffer to a 2 port buffer. Your system will remain almost exactly the same, the efficiency will take a jump in the right direction.
This is similar to 4 port but also very different in operation. So the install will look like this
So primary pump and buffer temperature is controlled by the heat pump and the secondary pump by the heating system. Flow through the system is very different for the 4 port. All water bypasses the buffer, unless the secondary system demand is less than primary flow. Then flow will go through the buffer. The heat pump will continue to run when the secondary pump demand goes off, to charge the buffer. Once there is a demand for heat on the secondary side, heat is immediately available from the buffer.
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