My ASHP Journey in Bonnie Scotland.

QrizB

cannugec5 said:

We don’t have any other ‘control equipment’

There should be a controller/programmer for your heat pump, where you can set flow temperatures and weather compensation curves and all those things?

matelodave

As @QrizB says, the heatpump will have its own controller which allow you to adjust the flow temp, weather compensation slope and probably a schedule timer - what make and model is your heatpump

cannugec5

We have a Grant Aerona HPID17R32. 

We have a controller by the cupboard that contains the water tank. It does not appear to be designed for customer use - with a warning that it is set by the installer. 

The documentation states that weather compensation has been set by the installer. 

It all works perfectly fine. We were very happy last winter, and the costs were less than the previous first winter with the ASHP. I’m just now looking at optimal efficiency now that I can actually monitor usage. As Cosy is advertised as a Heat Pump tariff I wondered if I was missing something. 

cannugec5

matelodave said:

TBH a Hive is probably not the best way to control a heatpump, Its a bit like controlling the speed of your car using the ignition switch rather than the accelerator. The house temp just bounces up and down and the heatpump cycles rather than adjusting the flow temp to suit the weather.

I dont know what facilities your heatpump controller has, but my 15 year old Daikin has the facility to program different temps at different times during the day (and night) whilst using weather compensation. So it would be reasonably easy to programme in a set back during during peak times and a bit of a temperature boost for an hour or so during the off-peak times.

I dont have Cozy as I wouldn't have a happy household and would never manage to get SWMBO to use power at off-peak times but I can control my temps to set back overnight and up it a bit for an hour before we get up.

I dont vary the flow temp by more than 3-4 degrees. I have disconnected all the external controls and zone controllers so the system gently idles at the lowest temp I can get away with (bearing in mind household harmony) and it just tries to maintain an even temp (except overnight when the flow temp is set back by 3 degrees and it drops a bit).

It actually uses less electricity as its idling most of the time with slow changes in the flow temp (use the car accelerator analogy) and the house is warm and cozy all the time rather than having the temp drop over night and then the heapump flogging its heart out to get it back up to temp

I’ve been thinking about the car analogy and it does make sense to me. However I don’t think I should play around with the controller. I don’t have the knowledge or expertise and really don’t want to compromise the set up. 

Can you explain how your system ‘gently idles away’? Does this mean, via your controller, that you have it on but without a specific heat target, so that it simply remains on until you tell it otherwise? Are you making frequent adjustments  or does the weather compensation work very well? 

matelodave

When I got my system installed some 15 years ago it seemed like a really good idea to have each room as a zone (we have underfloor heating and each room is a zone with its own programmable thermostat) and I spent weeks trying to get it optimised using the stats to turn the rooms on and off according to their use - Lounge all day, bathroom and bedrooms in the morning and bedtime, dining room and kitchen at meal times etc and several degrees setback over night. Also the flow temp was fixed at 40 degrees

All that happened was that the heatpump cycled as the stats switched on and off, when the zone valves closed it reduced the flow so the flow was diverted via the bypass valve which caused more cycling and TBH because of the slow response of the heatpump combined with underfloor heating it took ages to reheat when the rooms cooled down overnight and it used nigh on 5000kwh a year in the first year (it was also pretty cold that winter)

Over the years I've disconnected the zone actuators, disable all the thermostats, tweaked the weather compensation slope until it felt like it was balancing the building heat loss (approx 42 degrees when it's -5 outside and 25 degrees when its 15 degrees outside) - we have uplifted it a couple of times if its got really cold or we've stayed up past midnight, but the controller reverts at the next time period.

The system controller now runs the heating when it feels the need with a set back of 3 degrees overnight from 21:30 to 06:00. The house is now warm and cozy all the time as it never gets cold, the heatpump still cycles just a bit but most of the time it really is just idling rather than going full blast every time a thermostat called for heat.

The flow temp now sits around 28-35 degrees depending on how cold it is. We heat the hot water around lunchtime to just 45 degrees and the 200 litre tank gives us enough water for our night time and morning ablutions.

Since doing all that I guess we use around 4000kwh a year for heating and hot water and that's been pretty consistent for the past five years. It doesn't need fiddling with since I got it sorted out, it just gets on with it.

In fact its was down to 4.7  degrees last night and its been pretty cold for several mornings this week. The floor is just about lukewarm with a flow temp of around 28 -30 degrees. The house temp hasn't dropped below 19 degrees which means I've got a happy wife rather than the whinging about being cold that we used to get.

We've got a couple of these that we can use to monitor a record temperatures which helps with the balancing of room temps against weather compensation - there's also one outside which gives the same temp readings as the heatpump's outside temperature display - https://www.aliexpress.com/item/1005007755890938.html? They are cheap but do the job Also avaiable from Amazon - https://www.amazon.co.uk/Temperature-Hygrometer-Thermometer-Compatible-Intelligent/dp/B0BMLMQ3RM?

cannugec5

Thanks. That’s all very interesting. 

2024 was our first full year with a heat pump and we used approx 5000kWh more than Pre Heat Pump days. Month on month in 2025 so far, we have used less than 2024 so hopefully we will see that continue to the end of the year. 

One of the unresolvables is the differing preference between my husband and I. I’d turn the heating down, day and night. He feels the cold. He does wear a sweater most of the time, so it’s not as if he’s running around feeling cold but inappropriately dressed! We’ve been married 40 years so it’s not going to change:) 

cannugec5

As the year has ended I check my stats. 

In July 2025 we finally got a working smart meter and Cosy Octopus TOU tariff . 

In 2025 we used 1100 kWh less than the previous year and spent £386 less. 

2026 should be even better as it will be a full year. 

I’ve been telling an anti Smart meter friend and think she might be converted:) 

Reed_Richards

I would have thought that the best way to operate with a simple thermostat controller and a time of use tariff is to set the desired temperature to be "high" when electricity is cheap and "low" when it is expensive.  That way the heat pump is on as much as possible when it's cheap to run and as little as possible when it's expensive.  But I can't remember if Hive is one of those "learning" controllers that would fight you if you tried to do that.  And it might be uncomfortable if the resulting temperature fluctuations in your house are too large.

For example, I get cheap electricity from midnight to 06:00 so the cheapest way I could operate my heat pump would be to make my house as warm as possible at night (midnight to 06:00).  But that is actually when I want the house, particularly the bedrooms, to be cooler.  So I compromise and stop my night-time set-back at 03:30.         

NedS

cannugec5 said:

One of the unresolvables is the differing preference between my husband and I. I’d turn the heating down, day and night. He feels the cold. He does wear a sweater most of the time, so it’s not as if he’s running around feeling cold but inappropriately dressed! We’ve been married 40 years so it’s not going to change:) 

Welcome to the club!

We have found a heat pump better in this regard as it's a more comfortable stable heat compared to a traditional boiler which results in larger temperature swings accentuating the differences between feeling too hot or too cold, and made worse by the resulting thermostat wars. The good thing is nothing happens quickly with an ASHP, so the temptation to just notch up the thermostat a bit when your partner isn't looking is largely removed.

We find the steady constant temperature tends to result in both partners adjusting to the new steady state once a compromise temperature is agreed upon (I want 19C, wife wants 21C, so we settle on 20C)

cannugec5

Reed_Richards said:

I would have thought that the best way to operate with a simple thermostat controller and a time of use tariff is to set the desired temperature to be "high" when electricity is cheap and "low" when it is expensive.  That way the heat pump is on as much as possible when it's cheap to run and as little as possible when it's expensive.  But I can't remember if Hive is one of those "learning" controllers that would fight you if you tried to do that.  And it might be uncomfortable if the resulting temperature fluctuations in your house are too large.

For example, I get cheap electricity from midnight to 06:00 so the cheapest way I could operate my heat pump would be to make my house as warm as possible at night (midnight to 06:00).  But that is actually when I want the house, particularly the bedrooms, to be cooler.  So I compromise and stop my night-time set-back at 03:30.         

This  is what I have done - told Hive to heat during cheap “cosy” periods and avoid the expensive 4-7pm period. In fact I found the best schedule on the Octopus website, after playing about trying to find the right one. 

I have switched off the Hive ‘ready by’ function as this was confusing me and confounding my attempts. I want the heating on when it’s cheap, not to be nice and warm ‘ready for’ the cheap periods.