Air Source Heat Pumps

gterr

Thanks for the responses. Yes, absolutely right. This is a new build and we were left with comprehensive literature for the pump which is difficult to decipher. We called back the plumber but he couldn't really help, having set it up with the manufacturers recommended settings. He understands his own plumbing, but can't/won't get involved with the computer settings.

We do have a 'primary store' in the loft which is an extra tank of hot water, intended to address the issues you've raised.

The purpose of the heat curve is to allow the flow temp to change according to the outside temp, so in theory the system should work efficiently in all weathers. The recommended heat curve settings are different for U/F only and U/F plus rads, so someone has thought that they've provided for this.

I do have access to Worcester techincal help via email, but it takes a couple of days to get a response to each question, and no real discussion happens, which is what I need really.

I am going to experiment with the indoor temperature sensor. I can't see why we have this when we have stats in every room. The sensor 'influences' the heat curve in some way not explained. Since it's situated in the warmest place in the house it may perhaps be limiting flow temp in an unfortunate way. It's possible to 'reduce the influence' of this indoor sensor - perhaps even switch it off altogether - and then the heat curve will depend on the outside temp only. I'll see if this improves things.

And, yes, the whole point of opting for an ASHP was for economy, so I really don't want to run the pump with inefficient settings.

Thanks for your time.

richardc1983

gterr wrote: »

Thanks for the responses. Yes, absolutely right. This is a new build and we were left with comprehensive literature for the pump which is difficult to decipher. We called back the plumber but he couldn't really help, having set it up with the manufacturers recommended settings. He understands his own plumbing, but can't/won't get involved with the computer settings.

We do have a 'primary store' in the loft which is an extra tank of hot water, intended to address the issues you've raised.

The purpose of the heat curve is to allow the flow temp to change according to the outside temp, so in theory the system should work efficiently in all weathers. The recommended heat curve settings are different for U/F only and U/F plus rads, so someone has thought that they've provided for this.

I do have access to Worcester techincal help via email, but it takes a couple of days to get a response to each question, and no real discussion happens, which is what I need really.

I am going to experiment with the indoor temperature sensor. I can't see why we have this when we have stats in every room. The sensor 'influences' the heat curve in some way not explained. Since it's situated in the warmest place in the house it may perhaps be limiting flow temp in an unfortunate way. It's possible to 'reduce the influence' of this indoor sensor - perhaps even switch it off altogether - and then the heat curve will depend on the outside temp only. I'll see if this improves things.

And, yes, the whole point of opting for an ASHP was for economy, so I really don't want to run the pump with inefficient settings.

Thanks for your time.

Try overriding the room temp sensor by setting it to the max setting of 30c this way your rad stats control the temp of the rooms.

[Deleted User]

Now we know you have a heat store in the loft some of my points are still valid. The heat curve is part of the problem in that the store is heated to variable temps but also having many stats all calling for heat at different times really can start to complicate issues.

Solutions could include running the ASHP at a constant temp e.g. 50c and mix down to required temps... COP would be be lower but it's not as simple as just that so getting the original installers back is a must.

Cardew

jeepjunkie wrote: »

I agree the system here is basically a compromised design. Looks to me like the sort of system that would work fine with say GCH but not a heat pump. From what you are saying I'm guessing manufacturers would have to sign off designs a prior to install?

.

Essentially all ASHP systems should have a 'bespoke' installation.

Not only are the sizes of houses and their rooms different, so is the standard of insulation.

You may use your upstairs rooms purely as bedrooms; I might want them as a TV room, or 'living room' for teenagers or elderly relatives and thus reach a higher temperature.

There should be flexibility in the design to cope with the above.

At the moment the major manufacturers sell the components to an installer, and the customer takes pot luck. As the EST 12 month trial indicated 25% of the ASHPs had system COPs of between 1.2 and 1.6!!

IMO the major manufacturers(Mitsubishi/Daiken) etc should have their own installers(obviously sub-contracted firms) and they themselves take responsibility for the installation and give some guarantee of performance.

At the moment just from evidence on MSE it is apparent that ASHPs are being installed in unsuitable properties and/or with unsatisfactory installations.

Has anyone heard of an installer telling a customer that their house is unsuitable for an ASHP?

[Deleted User]

Being a new build the house does sound suitable and there is nothing wrong with heat pump technology per say it's all down to the knowledge of the installers.

Being fobbed off beacuse they only understand the plumbing side and not the computer side of it is a joke and does not inspire confidence for future issues or even geting it resolved to satisfaction.

My owns ASHP performs absolutely flawlessly which is probably down to a simple design even though it may appear complicated on the outside. As with all 'simple' things in life a huge amount of time, research and design went into it and as Cardew correctly says this can be their downfall... Only a bloody expensive one

gterr

Just a couple of additional points since I'm out of synch with the latest postings:

I'm happy that our installation is appropriate: it's a new build with huge amounts of insulation. A 'proper' survey was done before the ASHP was chosen, and the manufacturers, Worcester-Bosch did send out their own engineers to commission it - last April. We, the customers, were not present since we had not taken over the house by then.

It is true that there are different levels of Menu on the computer. The simplest just allows you to view the temps (outdoor sensor, indoor sensor, hot water temp (for showers etc.), flow temp), also indicators for what's currently working (fan, compressor etc.). There's a global "room temperature" setting which you can adjust up or down by half degrees, and there's also the opportunity to request extra hot water (for multiple baths, showers etc.) which would use an auxiliiary electric heater (we've never needed this).

The second level is the Advanced Menu, where all the other settings can be adjusted. This _is_ intended for use by the customer, if needed.

Then there's a third Menu of settings for installers only.

The ASHP does come with an array of mixing valves, but I'm afraid I don't know what these do. Then there's this additional mixing valve installed by the plumber near the U/F manifold, set to 50 c, and I still don't know what this is supposed to regulate.

It is very true that every house is different, so the settings ARE likely to need adjusting to suit. I do feel let down that there isn't some sort of service offered by the manufacturer: perhaps a visit at, say, a couple of months after commissioning, at which all these issues could be addressed. I am not a stupid person - I have a PhD in biophysics - but I find it impossible to get to grips with this. It's so frustrating because I'm quite sure the system CAN be set to do what we want AND be efficient. I'm not confident that left to my own devices I'll ever achieve this.

Cardew

gterr wrote: »

I am not a stupid person - I have a PhD in biophysics - but I find it impossible to get to grips with this. It's so frustrating because I'm quite sure the system CAN be set to do what we want AND be efficient. I'm not confident that left to my own devices I'll ever achieve this.

Indeed, and the difficulty is how will you ever know what is the optimum efficiency?

This is especially so when(hypothetically) your chosen settings lengthen the time/frequency of defrost cycles.

You have no possibility of working out the overall COP.

[Deleted User]

Simply put... your ASHP produces 'low grade' heat say for example 25-30c for the bulk of the year on the heat curve primarily for UFH.

Any mixers on the system will not be doing anything. The only time they are likely to be doing anything is in the thick of winter when say the ASHP is heating water to 50c which is ok for rads but to high for ufh so cold water will be introduced to mix back down to say 25-35c.

COP will drop in winter doing this though which is why I suggested fitting fan convectors as this would improve COP by running the entire system at a low temp. Which then sort of makes the heat store redundant... As this is all new its hardly what you want to do to a new system but increased knowledge may help you get somewhere with the developers...

An ASHP with a low COP will use a lot of leccy...

gterr

Thanks jeepjunkie.
Setting the heat curve as recommended for U/F plus rads, the flow temp will only reach 50 C if the outside temp drops to -24 C.

Even with the higher heat curve settings (the ones that currently allow my rads to stay warm) the flow temp would only reach 50 C with an outside temp of -13C. We are in the Highlands but on the coast. The lowest temp we got during the last 2 'bad' winters was -11 C on one occasion.


I have adjusted heat curve back to maunfacturer's recommended settings (V=20, H=55), and have turned the influence of the internal heat sensor down to 0 (off). I'll give it 48 hours and report back here what happens re my radiators.

Thanks for all the helpful ideas.

[Deleted User]

Great stuff, hope all the posts from everybody have helped

-11c won't bother a correctly sized/sited HP in the slightest.

Cheers