British Gas Heat Pump installations

Reed_Richards

I'm really glad you have made progress, @oliver1951.  If you get Weather Compensation really finely tuned (which may take some months, at least) then you don't need the room thermostat so you just set it to a temperature higher than you actually want the room to be, to ensure that the heat pump stays on.  But you might get a really sunny day and your room gets a lot of solar gain or you might have a party with 20 people in the room and either will cause your room to get hotter in a way that pure Weather Compensation cannot take account of.  So you set your thermostat to a temperature that is hotter then usual but bearable,  so that the heat pump turns off it it gets too hot. So that's where my 22 C came from, a temperature I thought was probably hotter than usual but bearable.  I'm pretty sure that is what long-term heat pump owner @matelodave does.

The exact Weather Compensation settings you need will differ for every different house so it is unlikely yours are exactly right yet.  In which case you may need to set your Hive room thermostat closer to the temperature you actually want whilst you are tweaking the settings to suit your particular house.  Anyway, at least you are getting downstairs heat now and that has to be good!        

oliver1951

Thanks @ReedRichards.

stripling

@oliver1951
7am update: It worked. So all rooms seem to be advancing on a common temperature. The downstairs rooms are now within a degree of the upstairs rooms. Weather today is going to be poor for solar energy ( thru the windows anyway) so perfect day for continuing to see what it does

Great news! Now you can tweak away by degrees with your weather curves to get a good efficiency v comfort balance. Enjoy your heat pump.   🙂

matelodave

As @Reed_Richards suggests that is exactly what I do. If the thermostat is set lower then the heatpump cant use weather compensation to control the temp of the house as it is being continuously cycled by the external thermostat which causes the heatpump to cool down and then run flat out until it gets back up to temp rather than idling gently.

I did have a power monitor on mine for a while when we first got it and the pump just cycled on and off with large power consumption peaks every time it restarted (the trace looked like a sawtooth) whereas now it just gently speeds up and slows down and the power consumption sits at a much lower continuous level (a gentle curve) = less strain on the pump as its not continually stopping and starting), lower energy consumption (no big power peaks) and more comfortable even temp all day.

By all means use the Hive as a time controller but even then if weather compensation is properly adjusted then it can take some time to achieve the desired indoor temperatures if you let the place cool down too much. In the end its a compromise between efficiency (ie lower flow temps for longer) or heating response which means a higher flow temp and therefore lower efficiency.

As suggested by @stripling above, set the weather curve as low as you can reasonably get it so that you can achieve and maintain your temps and recovery times. A lot will depend on your lifestyle to get it just right. It's a case of iterative tweaking - small adjustments allowing sufficient time to gauge the effect. The lower you can get it the slower it will be before you see the effect. I found it was more effective to turn it down until you weren't quite warm enough and then up just one degree at a time as you are trying to match the flow temp with the heat loss of of the house.

As we are at home all day we can let ours chunter away at a very low temp, usually around 30 degrees with it increasing to around 42 if it gets everso cold outside (-5), However the heatpump controller (not the stat) lowers the weather compensation slope overnight (21:30 to 06:00) so it does still run although at a lower temp and the place cools down a bit. It can still take until around lunchtime or later before the room temps have recovered (that's also due to the slow response of our underfloor heating, radiators might be a bit faster to react)

oliver1951

@matelodave . Thanks. Had a good day today, BG came along and we proved there is an issue with the Hive controller. Other than that thanks to @reedrichards suggestion , I am getting very even temperatures across the house. I am running it 24/7 and it’s running pretty evenly at around 400w per hour. Av outside temp is varying from around 12 c- 16c. I have the 8kw altherma 3. No idea if that’s reasonable consumption or not around 9.6kwh per day. Obviously that will go up as the weather gets colder. My flow temps are ranging from 24 to 29, which seems good. I have the standard curve at the moment which will need to be tweaked , it runs from 45 to 25, I understand 25 is the minimum, even though as noted above the system has registered a 24 LWT. I am using maximum offset now of 10, although I note it doesn’t actually offset it that much. I’m getting, if I’m to believe the MMI figures a heating cop of around 4.1.
 I use the totals since install figues, which seem to , at that total level, seem to be a little more reliable, and the usage figure seems to be about what I would expect going by my smart meter. Obviously I have no means of validating the produced figure.

its a little bit warm, hence why I have max offset, so my thought now is to lower the curve, maybe push it down to 40 at the top end . Not sure yet how to tweak it, so suggestions are very welcome, only need to get the temp down a degree or two. But honestly I don’t think I’ve ever experienced such a consistent and pleasant temperature. It’s quite a revelation.

oliver1951

I did another test today. Powered off all the heating, for 4 hours. Restarted after sunset, wanted to avoid any solar gain effects . I wanted to see primarily if there was going to be a spike in consumption, in say the first 30/ 60/ 90 mins. But no there wasn’t, it just kicked in and did its steady eddy of around 400w per hour and off we went. I was rather pleased with that. Because apart from anything else the temperature had got a little high and whilst in those 4 hours it only dropped back a degree it felt good. I think it must be because it’s weather dependent it doesn’t try too hard to get something up to some temp target. Which suits me very well. It’s been running (LWT) at about 26c. In the 3.5 hrs since turning it back on the temp has risen a reasonable 0.7c. And in that time outside temp dropped 1c. 

john-306

Interesting with you saying you didn't get a door in consumption when resuming heating.
I've got the same heat pump as yourself. Whenever mine resumes herein, be it after 10 mins or 6 hours, I get anywhere between 1 and 2kw consumption before settling down to around 300w.
Take this morning, heatpump been running at tickover lovely for hours, suddenly consumption spikes for no reason to 1.1kw then shuts off for 10 mins, upon resumption it spikes again to 1.6kw before settling down again. 

I've only recently installed Emoncms so still getting my head around all the data, but Cop at high 4s looks good.

matt_drummer

I have an 8kW Daikin.

They always start a heating cycle afresh, they never just resume where they left off.

The heating cycle always has around 20 minutes at the beginning at the highest flow rate and it then drops down over a further 10 minutes.

The heating cycle always starts with short period of warming the compressor with electricity consumption but no heat production.

My heat pump is fully MID monitored on heatpumpmonitor.org

All the current Daikin heat pumps behave this way.

The 9 to 16kW models will always stop and restart after 6 hours of continuous running, I think it is to do with compressor lubrication.

The 4 to 8kW models will run pretty much continuously.

When it is warmer outside, the heat pump will eventually, in most installations, reach a point where it needs to stop. Normally I see this when the house is warm and the overshoot has been used and exceeded, it stops the heat pump once you go 0.5c over the set flow temperature plus any overshoot allowed. This is usually preceded by a sharp but short increase in electricity consumption. The heat pump will then commence a new heating cycle from scratch 5 to 10 minutes later.

It is virtually impossible to get any real idea of what a Daikin heat pump is doing without some form of monitoring, be it ESPAltherma (which I don't think is very accurate) or a heat meter.

Daikin heat pumps do not like low flow temperatures, particularly when it is warmer.

I can run mine at about 27c at 15c outside but it doesn't like it. It uses just as much, if not more electricity than it does at 32c. If it bothers you, the efficiency is much better at low 30's than it ever is below 30, you don't use any more electricity but you do get more heat.

You will only realise this if you have some way of monitoring the heat pump in detail.

It is counterintuitive, I know, but these Daikin heat pumps run much better over 30c, they are more efficient, use less electricity and will run with longer cycles.

Trying to run at 26c flow temperature with these heat pumps doesn't work very well. It will be cycling like crazy and without any monitoring you may not even know it was happening.

matt_drummer

To expand a little on how Daikin heat pumps work.

They focus on return temperature.

If you set a flow temperature of say 30c, either by fixed lwt or a wdc, with a dT of 5c, then the heat pump will try to maintain a return temperature of 25c.

It does this by varying the flow rate to maintain the return temperature requested, in this case 25c.

If the return starts to rise the flow rate lowers, if the return falls the flow rate increases.

Once you are at the minimum flow rate there is nothing left to stop the return temperature rising.

Then the overshoot comes in to play.

Once the overshoot temperature is exceeded by 0.5c the heat pumps stops, waits a few minutes and then tries to run again.

The nature of the Daikin heating cycle means you start again at maximum flow rate. This creates lots of heat even though your heat pump has only just stopped due to excessive heat evidenced by the rising return temperature that caused the heat pump to stop.

The high flow rate in the new heating cycle makes the return rise again very rapidly and the heat pump has to stop again.

This continues over and over resulting in very short heating cycles of only about two or three minutes of heating and a break in between of about 5 minutes.

This is short cycling in the extreme.

At very low flow temperatures, below 30c, with higher outdoor temperatures, most heating systems will not be able to dissipate the heat produced during the aggressive start of the Daikin heating cycle.

I have very big radiators and improve my warm weather performance in two ways.

I don't try to run at inefficient (for Daikins) flow temperatures.

I also limit my flow rate using the MMI. I set it at the minimum of 60% and this limits the amount of heat I get at the beginning of a heating cycle.

That means I can, if i want to, get my heat pump to start and continue to run even if it is warmer outside because I am limiting the rise in the return temperature so that the heat pump doesn't shut down.

I also have an overshoot set at 4c which allows the heat pump headroom to complete the initial part of the heating cycle without failure every time.

I wouldn't advise this for everybody though.

As my maximum flow rate is now restricted to 60% I have limited the heat pumps ability to increase flow rate to maintain the requested dT between flow and return.

For this reason I run as radiators with a fixed dT of 10c. I never get this. What happens in my house is that the flow rate always settles to the minimum as the heat pump is always trying to get to the dT of 10c.

I run a pretty much fixed lwt and then my heat output varies with the heat loss of the house. As it gets colder the dT gets bigger because the heat loss of the house has gone up.

I only vary my flow temperature to suit the compressor, it likes to be under load, so I increase slightly as it gets warmer and turn it down as it gets colder. I always aim for the least electricity use and the highest efficiency.

It won't work for most people I admit.

You need to think of the Daikin compressor like a car engine, the best efficiency comes at a fixed load in a high gear. Driving fast (high flow temperature) uses more fuel, and driving slow (low flow temperature) uses more fuel.

With decent monitoring, it is easy to see when the compressor in the most efficient operating window.

Other brands of heat pump work differently. Daikins get to the set flow temperature quickly. Others don't. They build slowly and run at a fixed flow rate. That is why something like a Vaillant runs happily at a lower flow temperature than a Daikin.

Looking at other monitored heat pumps, I find that Daikins perform well at lower flow temperatures with lower outside temperatures compared to other heat pumps. Daikins don't do so well compared to others when it is warmer due to the dislike of really low flow temperatures.

My feeling is that Daikins are really good when it is cold and that is the best time as that is when you use the most electricity.


I hope that helps explain how a Daikin heat pump works, why a low flow temperature isn't advisable in terms of efficiency, why short cycles occur and why you really want to avoid them with Daikins.

I also strongly advise some sort of monitoring, what you think might be happening and the reality can be quite different.



 

john-306

Very informative thank you. 

I only mentioned about the restart consumption as Oliver said his didn't spike after 4 hours of being off. 

I'll try running at 30+ temperatures and see how that works out. 

I've got espaltherma set up, while I know some folks say isn't the most accurate,  it at least gives a baseline to work off.