Programmable TRVs with new High Temp Air Source Heat Pumo

[chris_j_hunter]

coil & location of heat-pump unit sound fine ...

to measure performance, you need to measure water temperatures in & out of the heat-pump unit, air-intake temperature to the heat-pump unit (all usually read from the control panel), power consumption (kW), and water flow rates (litres per minute, through the heat-pump unit) - without a full set of all these, you can’t evaluate performance.

Heat transfer being the product of temperature rise and flow-rate.

Doing spot-checks manually might work but, because things inevitably go up & down all the time, would be very rough & ready - continuous data-logging into your PC would really be necessary, with it combining the data & plotting graphs for you to assess.

Power & flow-rate meters are available, giving a number of pulses per kWhr & per litre ...

[chris_j_hunter]

Not sure I understand the graphs ...

First graph (energy demand against outside temperature) ... how to read it - the numbers on the horizontal axis don’t align with the tick-marks & seem rounded up & down, and the legends are unclear but, more than that, if the purple line is the energy the heat-pump will take from the mains in order to generate the heat given by the blue line at 65degC then, while the CoP at 7degC ambient is about 2.88, as per the blurb posted previously, the trend would be way too optimistic ...

Second graph (demand against system capacity) - again, how to read it - there are 8760 hours in a year, and basic seasonal variations seem to be absent (even allowing a roughly constant hot-water demand contribution throughout) ...

[heatingitaly]

re the issue of DHW generated by an immersed coil or a plate heat exchanger (PHE). The lower temperatures of heat pumps make the PHE absolutely neccessary as they have a smaller DeltaT so you can still keep working with the tank cooler. Think about performance - my PHE can deliver 40L/min and develop up to 160kW of power right up to the last drop of hot water from the top of the tank. The coil needs the whole tank to be hot - poor recovery times - and while it starts off being a low performer it gets even worse as it gets calcium deposits on it through low flow. No point in measuring performance if it doesn't perform!

[chris_j_hunter]

OTOH, high flow rates to & from a plate heat-exchanger could disturb the stratification ...

while long coils can be v.effective with v.little disturbance, because coil flow & tank water don't mix ...

indeed, coils that run the whole height of the tank, provided the flow direction is appropriate, can extract most of the available heat, even with tanks that are far from evenly heated - eg: with coil flow up the tank, as the water rises through the coil, it can collect heat all the way, from cooler bottom, to hotter top ...

plus, lower flow rates can allow the time for heat to get transferred - looking at our flow & return temperatures, it's clear our flow rates are a bit on the high side (ie: return temperatures not particularly close to tank temperatures)

[heatingitaly]

Chris you are quite right - the flow of the tank water through the PHE does destratify the tank but probably less than you might imagine. The moment when the hot water runs out with this arrangement comes fairly abruptly which implies that the tank remains stratified right up to the last few litres of hot. One disadvantage is that the flow through the PHE continues apace whether the actual use of the shower water is fast or slow. There are some pretty sophisticated solutions out there where pump speed varies to maintain the perfect output temp.... a good example is from a German co. called PAW.
Forgive me bintyandthebeast for veering off topic but I hope you find this useful. My favourite tank arrangement has 2 tanks. 1st one has a coil feeding the second which has a PHE. This enables really low ASHP delivery temps and also makes solar panels super efficient with a cold tank to deliver to. My solar panel pump runs all day and almost every day across the year.

[bintyandthebeast]

heatingitaly the info is useful, and I get what you're saying. We will, however, be sticking with a single tank and I'll see about getting the hot water to reheat during the day, unless there is an urgent demand to make use of the solar PV power we have available. The installers have advised they can set it up this way, so that should be good. I will keep my eyes open for some second hand electronic thermo valves to try them out, as I think they would be financially beneficial in the longer term, but spending in excess of £1000 for something more fancy, while being more fun, will never repay itself.