ASHP DIY Install

[andyrob]

This is my first post so hopefully it will attract a bit of interest.

I've just bought five 4.5kw ASHPs (Calorex AW4502) - all fairly new and taken out of a Social Housing Scheme as they were undersized for the houses to which they had been fitted - apparantly a common problem for this, the smallest Calorex ASHP.

So, I'm doing everything the wrong way round - making the buildings to which they are to be fitted suit the pumps. I'll post the issues I'm considering a couple at a time.

The first question relates to the replacement of the 134N gas with R407C. This will cost perhaps £500 per pump, parts and gas, and gives an additional 1kw of maximum output and better low-ambient temperature performance, albeit at the cost of a lower maximum output temperature. This can mean additional heating of the DHW is necessary (eg for legionella control). Can anyone comment on this factory upgrade - its performance, who can do it (in the East Midlands, UK), etc?

Secondly, for the first house, a four-bed, mid-terrace which is stripped bare just now (but it will be well insulated and have UFH fitted), I think two of these pumps will suffice in conjunction with two 5kw log-burners (one of which has a back boiler) which will be at each end of the ground floor. I'm thinking of connecting two pumps in series, though I could use one alone for DHW, and another for space (UFH) heating.

What would you do?

Andy

[Brian_UK]

The first thing I would do is to get the heat load calculations for the building absolutely spot on and based on the correct winter ambient temperature.

I would then ensure that the ASHP are capable of working and providing useful output at the winter ambient.

Full energy calcs then need to be done to compare ASHP/log burners running costs (honest cost not sales pitch cost) with the alternative fuels available to the site.

Getting these things wrong will create very expense running costs.

[andyrob]

At this stage I have no idea what the U-values and heat requirements will be. I just have a gut instinct as to the ball park figure at the moment - and I did acknowledge that this approach was all the wrong way round.

However, I know of many renovations and new builds - like those my ASHPs came from - for which software and other calculations have been done completely incorrectly. So one important step is to find someone who really knows their stuff in this respect. But only when I have nearly finished the structural stages of the renovation will I be able to have a stab at the heat requirements.

But to get back to the ASHPs, it was to give me the flexibility of another 1 kw per AW4502 heat pump, if I need it, that I was asking about the R407C (especially in the context of this forum) - and the general benefits of upgrading to that gas.

And a suggestion for the "connection in series" (or perhaps parallel?) question would allow me, using one ASHP unit, to have a nominal 4.5kw (or 5.5 with R407C) , or 9kw (11 with R407c) with two units - even 13.5kw (16.5) if I used three of the ASHP's together. This would allow me to match the ASHPs to the calculations of required heat loads when they are done.

The other reason I thought this approach could work is because it gives me more flexibility than the units in the standard Calorex range (4.5kw, 8.5kw, 11.5kw). Also, this is how large fossil fuel boilers - say in schools - are configured for efficient operation. Today, say, nine small boilers are often used when, in the past, only two would have been used for the same output; the benefit of sophisticated controllers, of course.

Andy