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Fine tuning your ASHP performance

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(@heacol)
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@editor By the way, Performance of the heat pump (COP) has nothing to do with how leaky your house is. It has to to with the distribution system and how you controll it.

Professional heat pump installer: Technical Director Ultimate Renewables Director at Heacol Ltd


   
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Mars
 Mars
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@heacol, that's a good point about COP and leakiness.

Our issue was heat emitters - when we added Stelrad K3s it made a world of difference in the coldest rooms in the house. K2s in the southern end have been adequate, and UFH has always been great. 

Derek has been hammering at me and our weather compensation which we haven't been able to get working properly because the main controller (which reads the temperature) is inside the HW cupboard and it's always very warm in there. So I just set our flow rate manually. It's actually at 40C now (it was set to 35C), and will try to get through the winter at that temperature. We also have a bivalent system, so I've set up our oil boiler to take over heating when temps drop below 8C – the only reason I've done this is because of the insane price of electricity, so it's a bit of a balancing act. The oil boiler has been set to its lowest possible temperature to allow it to condense. 

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(@derek-m)
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Posted by: @editor
Posted by: @heacol

@editor Low flow temperatures = low bills. It realy is that simple.

Fabric first to achieve low flow temperatures I guess. Our insulation is good to very good, but we still leak some heat. Getting better though.

Hi Mars,

I am beginning to wonder if anyone bothers to read the information that I provide. Having been a Control Systems Engineer for over 50 years and worked on and designed systems for power stations and oil and gas processing plants, thermostats would only be used on the systems of low importance. The problem with using thermostats in home heating systems is that they normally have a deadband of 1C, which means that to maintain a comfortable temperature within the home, they are normally set higher than would need to be if continuous process control was used instead of a thermostat.

To confirm the point that Brendon and I have been repeatedly making, for maximum efficiency an ASHP needs to be operating at the lowest water flow temperature that is consistent with maintaining the desired indoor air temperature. At the moment, with an outside air temperature of 12C, our radiators are cold to the touch, with our heating system in full operation maintaining an indoor temperature of 21C. When the outside air temperature falls to 6C, the radiators are only just warm to the touch.

If you take the trouble to look at the spreadsheets and results that I posted several weeks ago, you will see that ASHP efficiency is most affected by outside air temperature, indoor set temperature, heat loss (level of imsulation) and size of heat emitters.

Even the most expensive, supposedly intelligent heating controls, are not often used correctly with heating system that employ an ASHP.

 

This post was modified 3 years ago 2 times by Derek M

   
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Mars
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@derek-m, I always take on board what you write. The issues that arise, in our case anyway, is that we've asked Global Energy Systems several times to activate weather compensation and they say that due to the way that our system was installed and wired (as a retrofit) it's not possible. We did try to it in that mode a few months ago (when you first suggested it) and it didn't work at all well. So we've reverted back to manually tweaking it. 

The decrease in flow from 45C to 40C has resulted in our COP going up to 3.1 from 2.7 – the house is plenty warm at this flow temperature. I suspect a drop to 35C may be a stretch a too far at this time of year. 

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(@heacol)
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@derek-m Thanks, I also feel like I am banging my heat against a brick wall. However, If one person listins, they may tell another and maybe the mssage will get out.

Professional heat pump installer: Technical Director Ultimate Renewables Director at Heacol Ltd


   
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(@heacol)
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@editor Mars, Maybe you need to re-design your system. There is probably not much to alter to get good performance. If you send me some information, I will help.

Professional heat pump installer: Technical Director Ultimate Renewables Director at Heacol Ltd


   
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(@heacol)
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@editor Weater compensation has nothing to do with the internal temperature. Do you have timers, TRV's on all radiatrs and a buffer tank or system seperation with 4 pipes?

Professional heat pump installer: Technical Director Ultimate Renewables Director at Heacol Ltd


   
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Mars
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@heacol. Thanks Brendan. We probably have too many controllers and smart thermostats, which is probably an oil boiler mentality, and this prohibits us from having a single controller which could make weather compensation work. I also don't know how good Global Energy System's weather compensation logic is to be honest.

Another good example of the importance of system design – ours was "designed" by the sales guy, and this is an issue that the industry is also facing in my opinion. Systems that are sold by sales people, and that are installed by companies that take the sales reps 'recommendations', which leads to systems that are not fully functional.

 

 

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Mars
 Mars
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Posted by: @heacol

@editor Weater compensation has nothing to do with the internal temperature. Do you have timers, TRV's on all radiatrs and a buffer tank or system seperation with 4 pipes?

Not sure what you mean by timers. Smart TRVs on all rads. Yes, we have a buffer tank. We also have three smart thermostats for UFH (in three zones) and three smart thermostats to call for heat for radiators. 

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(@derek-m)
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@editor Hi Mars,

Sorry to hear about your foot, hope that it heals quickly.

I fully appreciate your problem in that your controller has been incorrectly located, but your installers should have been aware that this would pose a problem when they installed it. It is also bad practice to install electronic equipment in warm locations, which can adversely affect their operating life. For large control systems the panels would be located in air conditioned rooms.

Some of the other manufacturers provide remote sensors, both hardwired and wireless, you could ask your supplier if they can provide such a device. The alternative would be to relocate either the controller or the internal sensor.

For optimum efficiency of your ASHP, you should lower your water flow temperature to a level at which your ASHP is operating more frequently, for longer periods of time, and only increase the water flow temperature setting when it can no longer meet the heat demand. At the end of the day it is your choice.

My earlier comment about being ignored is in relation to quite a number of posts to which I have responded recently and there has been no response. I therefore wonder if I am wasting my time when there are still members who continue to switch the heat pumps on and off.


   
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Mars
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Posted by: @heacol

@derek-m Thanks, I also feel like I am banging my heat against a brick wall. However, If one person listins, they may tell another and maybe the mssage will get out.

I appreciate your efforts and patience – when you're familiar with the way something works, it's easy to get frustrated when people don't get it. Heat pumps, maybe because they're not always installed properly, take getting used to. For us, it's been a huge learning curve, and I see comments all the time where homeowners are tweaking them because they're not running as they should. But I can understand your frustrations. 

I think more companies should be forced to provide 'designs' with their proposals, as opposed to a sales guy (I speak to our experiences) looking at the rads and house and saying, "yeah, no problem, the heat will replace your boiler. No problem." When the system's installed, its only then that the issues surface. 

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Mars
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@derek-m, thanks Derek. In our case, the installers asked us if we wanted to "keep things as they were" – the answer from us was yes, because this is what was recommended to us. So they replaced the boiler controller with the heat pump controller – in hindsight, it was the easiest solution with the least amount of work which is why they were happy to do that. Locating the heat pump controller to say the hallway would have been a lot more work, which was never suggested or recommended at any point.

Essentially, we had our oil boiler replaced by an air source heat pump, with no other changes to the system. And this is not the right approach, but as homeowners that know very little about such matters, you rely on the expertise of installers – this is also why we went down the MCS-accredited route. 

Much more heap pump education is required to empower homeowners in my opinion.

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