(basically primary runs now in 22mm copper and buffer (100L) turned in to a volumiser)
So on the ASHP side of the buffer was a UPM3L 15-75 130 and on the house side was a UPS3 15-50/60 130, this gave a flow rate of 870 litres/hour. No idea what the house side was doing, but was a fixed speed.
Since changing the buffer into a volumiser flow rate has dropped to 650 litres/hour, which would probably do for most of the year as it give equates to 3.7kW of heat. However this morning with it being colder, my ASHP was outputting 5.5kW of heat, so quite a bit of that wouldn’t have made it around the heating system.
My ASHP doens’t have an internal pump, so have been researching today what pumps generally come fitted in ones which include a pump. It would seem some come with a 15-105 130, one of these would be a straight swap and relatively easy to replace the existing. The question is would it be up to the job of delivering 870 litres/hour ?
The height from the ASHP to the highest point of pipe work is circa 7m (in 28mm). The house is then fed by a single run of 22mm copper 38m in length with 10 90˚ bends in it till the final radiator (14 radiators in total).
Or does anyone know of a online tool that will work out pump sizing requirements based on the length of pipe runs, height and number of radiators and bends ?
The heat will still have gone into your house, the DT will just be wider. This may not be a problem, I’ve seen heatpumps running at a DT of 7-8 without a problem. DT5 is only a rule of thumb and not a strict requirement.
Looking at your data from yesterday morning I can see you had a DT of 7, the heat meter is reporting a peak of about 5.5kW, so this energy must have gone into your house.
The flow rate you’ve currently got will probably be fine, a larger pump will use more energy. Is there anything you can do to reduce pipework restrictions? Have you tried opening up rad lock shields and ensure all rads are switched on?
I think Gundfos have some resources for choosing pumps, I’ve not tried these myself:
DT7 isn’t so bad like you say and I don’t think the ASHP put’s out much more than 5.5kW. Though I can easily turn the volumiser back into a buffer (via valves).
Yep all rads are fully open.
Pipework wise, could upgrade from 22mm to 28mm between 12-24meters. Though I could use MLCP, which would reduce the number of hard 90˚ bends at least, more sweeping bends and easier to install.
The other option, but probably a bit extreme and more costly is to route the 28mm from the ASHP into the airing cupboard (as opposed to the attic -w here it goes now), swap out the DHW cylinder for the buffer/volumiser and get a new DHW cylinder to go in the attic instead (the current 140L one is far from ideal for 4 people).
I’ll have a look for the vids from Urban Plumbers.
So as an update incase someone has a similar issue (though unlikely)
I came across this site earlier today which is very useful and informative.
I then started looking at MLCP Pipe and ended up speaking with the technical department at https://www.novatherm.co.uk/ who confirmed with me that the 32mm MLCP has a minimum internal diameter of 26mm (including all 32mm fittings). Which isn’t far off 28mm copper, but has the advantage of knot needing 90˚ bends.
My idea now is to run this MLCP in 32mm for for about 28m of the run, reducing down to 22mm copper and having one equal tee to feed the existing 22mm copper which will be capped off one end. This will mean (as a volume of radiator water) the main run will now be feeding 60% and the T will be feeding 40%. If I’ve understood the heatpumps.co.uk page that should then restore the the 850 flow rate. No idea when I’lll get round to it yet, but is circa the same cost as a newer pump. So worth it for the learning experience if nothing else.
Agree, I don’t think a higher flow rate and a lower DT will achieve any better performance. A larger pump will be a slight detriment to performance since it will use more power. Reducing pressure loss will mean the current pump has to work less hard, therefore using less power and potentially increasing lifespan, but probably not worth the cost and effort.
To answer some questions, it’s been an ongoing learning curve for the last couple of years. after the install (at great expense), which basically didn’t perform and couldn’t keep the house warm during winter.
So the I thought the buffer to volumiser would be the last thing that needed doing to have a system performing reasonably well. I’m not a COP chaser lol wrong house and no knowledge to get anywhere near the top
I will hold off any further tweaks, for the time being and see what occurs with the DT when it is properly cold.
Main reason for this post was that the current setup is making the pump is wor pretty hard, which is what it is, I guess.
