ASHP - advice please

We’re in the market for an ASHP to replace an oil boiler and have the results from an expert heat survey which suggests a 15/16kW unit is required.

Annual space heating needs are forecast to be 7460kWh (electrical) and hot water 2299kWh (electrical) – 5 people resident.

The house has underfloor heating on the ground floor and rads on the upper floors.

We’re currently on Octopus GO (7.5p for 4 hours then 38.94p for 20 hours) and are making good savings by EV charging and PowerWall battery charging at night.

Which brings me to my questions:

Is there a way to force the ASHP to do its hot water heating cycle during the cheap rate night 4 hours? And if so how?

Is there a way to use the hot water tank as a kind of buffer releasing heat to the space heating circuit during the high rate 20 hours? And if so how?

Thanks in advance for any advice/comments.

This depends on the ASHP system. In principle it should have a timer function to achieve this requirement.

It is unlikely that there will be sufficient hot water in the tank to maintain sustained heat required to heat the house. A better option would be to find an electricity provider with more low cost hours - 4 is hardly enough to do anything useful, for example with a typical EV charger, 28kWh charge max.

From a distance, and reading all the exploits on here, my feeling is that you always want to have the HP feeding a tank, then draw off from the tank what you need.

If connected directly to the heating circuit and if your requirement for heat is marginal, the ASHP will tend to short cycle. If you are drawing the heat off the tank, this short cycling will be reduced as the HP heats the tank and the heating gradually depletes the tank before the HP kicks in again (long cycles).

The UFH manifold should be a blending type manifold, so only draws heat from the tank slowly keeping the UFH temp lower than it might otherwise be.

Radiator circuit is the same (blend flow with return for target temp), but at a higher flow temperature. If the heat demand is high, you might be drawing off from the tank as much as the HP can supply. Actually, if you need a bit more heat, you can drive up the HP Flow temp to match (of course at the expense of the COP) - but it is flexible.

I’ve got an Akvaterm Solar Plus Tank connected to a boiler and connected to UFH (no Rads & no Thermal Solar) and a DHW coil. The tank has a baffle about 1/3 down to aid stratification. My intention is to modify my connection from the boiler to the tank as I have realised it is not the best way. This modification will then work with an HP eventually.

The tank has 2 x sets of takeoffs from top/middle/bottom. I currently use one set for the UFH (4 port mixer that is actually largely redundant). The other set currently draws off middle and supplies the top from boiler. This I will change by brawing from the bottom and adding a temperature controlled shuttle valve to feed the bottom 2/3 when below my DHW temperature and the top when above that set temp. Obviously a boiler is most efficient at a slightly higher temperature than a HP.

So, that’s my solution. For a retrofit, the big tank may not be an option :slight_smile: . YMMV

This is exactly what I do with my NIBE heat pump. I’m also on Octopus Go and I have the Hot Water re-heat ‘blocked’ in the heat pump controller from 04:30 - 00:30 so it only kicks in at cheap rate.

Best to check the controller manuals for any heat pump brands you’re considering to ensure they provide the options you need.

Of course, for this approach to be successful you need enough stored hot water to satisfy all the demand in the remaining 20 hours, which might need a big tank…

Hello, I have just installed a 16kW Samsung Gen 6 unit. I only finally commissioned it on the 24th February, so I am at an early stage of understanding how it is performing.
So more comments later…
But for now:-
The ASHP is connected to 5 U/F heating manifolds, which have in turn 18 separate heating zones my first impressions are the lower supply temperature works a lot better with the U/F heating and now the house has heat soaked, the electricity energy consumed has dropped from 4kW, to currently a continuous ~2kW. The hot water and radiator circuits are now entirely separate and remain connected to the gas boiler.
The ASHP installation is fitted with a 100 litre buffer tank, so I need a greater understanding of how this has affected the CoP of the overall cycle, but what I do know at the moment is the buffer tank has introduced a 2 degree step between the output of the ASHP and the input temperature of the heating circ pump.
I also use Octopus to charge batteries during the 4 hour period at night and heat the H/W tank
But any questions about the design, please forward.

Also for others who have installed a Samsung Gen 6 unit, with and without a buffer vessel:-

  1. What CoP are you achieving using the Samsung data and have you fitted any other instruments to more accurately measure the CoP and how do the results compare to the Samsung unit?
  2. Have you any temperature data, showing the temperature step caused by the buffer tank.