Optimising a heat pump

NedS

70sbudgie said:

On trying to find out more information about air changes, I came across this interesting article about a change to the ventilation calculations for an MSC compliant design from this June. 

https://heat-box.uk/en-gb/blog/post/new-mcs-requirement-heat-loss-calculations-must-follow-new-standard-from-june-2025

Hopefully this will help MCS heat loss calculations result in more realistic values.

Reed_Richards

My MCS calculation must have overestimated my heat loss because it turns out I can operate my heat pump at lower water temperatures than anticipated.  So that's not really a bad thing.

70sbudgie

Reed_Richards said:

My MCS calculation must have overestimated my heat loss because it turns out I can operate my heat pump at lower water temperatures than anticipated.  So that's not really a bad thing.

As I understand the article, that sort of over sizing is common when using the 2003 version of the BS and why the 2017 version is now being mandated.

NedS

Reed_Richards said:

My MCS calculation must have overestimated my heat loss because it turns out I can operate my heat pump at lower water temperatures than anticipated.  So that's not really a bad thing.

Same here @Reed_Richards. So far I've run my radiators at a flow temp of 32C all winter, only turning up to 35C on the coldest of days, and to counteract any temperature drop having switched off during the 4-7pm peak on the Cosy tariff. This is helped by having large enough radiators to be able to emit sufficient heat at such low flow temps.

Some of these Octopus ASHP installs with a flow temp design of 50C and no radiator upgrades worry me as it's not a great starting point for low running costs.

Reed_Richards

NedS said:

Some of these Octopus ASHP installs with a flow temp design of 50C and no radiator upgrades worry me as it's not a great starting point for low running costs.

Well Octopus are in the business of selling you electricity.  They can sell you more electricity if you get a heat pump and more electricity if it isn't as efficient as it might be.

Alnat1

Reed_Richards said:

NedS said:

Some of these Octopus ASHP installs with a flow temp design of 50C and no radiator upgrades worry me as it's not a great starting point for low running costs.

Well Octopus are in the business of selling you electricity.  They can sell you more electricity if you get a heat pump and more electricity if it isn't as efficient as it might be.

But their heat pump installations are so cheap compared to other companies that you can to buy an awful lot of electricity with the money you save. TBF, you don't even have to be an Octopus customer to have one of their ASHPs fitted

70sbudgie

In trying to optimise my HP at design stage, Iasked the designer what operation they had allowed for. We have 2 UFH zones and a radiator zone and I can't get my head around the Ecodan data book section on controls in particular how the adaptive temperature (weather compensation) would work with 2 zones (in comparison with my current 3 zones).

This is their response:

The Ecodan systems have an adaptive heat curve capability (room setting), meaning we can run zone 1 on the adaptive curve for the radiators, and selected a fixed flow temp for your UFH. Your existing controls will work the UFH the same way as you do now, the Ecodan will only see it as one zone, but it will function as two. The other zone will be a Mitsubishi stat for the radiators.

Could anyone that has UFH and radiators comment on how they use weather compensation?

Reed_Richards

I don't have UFH and radiators, just radiators.  But the way it could be done is for the output water temperature to be set by weather compensation when the radiator zone is demanding heat but to be a fixed temperature when the radiator zone is not demanding heat.  This assumes that the WC temperature will be higher or equal to the UFH zone temperature so the UFH always gets water that is at least as hot as it needs.   

70sbudgie

Reed_Richards said:

I don't have UFH and radiators, just radiators.  But the way it could be done is for the output water temperature to be set by weather compensation when the radiator zone is demanding heat but to be a fixed temperature when the radiator zone is not demanding heat.  This assumes that the WC temperature will be higher or equal to the UFH zone temperature so the UFH always gets water that is at least as hot as it needs.   

If I am understanding this correctly, it means the room thermostat for the radiator zone, would need to be the one that works with the weather compensation? Hence it is that one that is suggested as being replaced by the Mitsubishi stat? 

How would the radiator zone call for heat - I thought that the way to make the weather compensation more efficient (and avoid short cycling) was to not use a room stat? Or, by having additional zones, will the short cycling be avoided anyway, because there is always demand?

Reed_Richards

Hard core weather compensation avoids the use of a room thermostat.  This should be most efficient if you want your house to be at the same temperature 24/7 but if you don't then it's harder to achieve.  If you don't want your house to be the same temperature all the time you are likely to need zone/room thermostats.  Using a night-time setback could reduce your overall energy use.  And energy use does not necessarily equate to energy cost if you are on a time of use tariff.

Some heat pumps allow you to change the weather compensation settings to give you a night-time setback; mine (LG) does not.  And if you use a night time setback it will take a long time to get the house back to the daytime temperature because you are supplying only enough heat to maintain the daytime temperature (unless you use Load Compensation).  I use a night time setback but turn my heating back up to daytime temperature 2.5 hours before I get up, and that's with just radiators.  UFH typically responds so slowly that you pretty much have to set it to give you the same temperature 24/7.
  
Any room thermostat will work with weather compensation (or vice versa).  If you're doing it hard core just set the thermostat to a couple of degrees above the temperature you want in order to cope with solar gain or crowded parties.  But to also achieve Load Compensation you would need the heat pump manufacturer's own brand.  Load Compensation would give you heating that is more responsive but at the expense of being a bit less efficient.

It's impossible to avoid cycling in milder weather when the heat demand is less than the minimum your heat pump can provide.  Whether those (or any other) cycles are short depends on whether the heat pump controller manages the cycle time.  My Drayton Wiser third party controller does this but I don't know about others.