Posted by: @batpred

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Posted by: @temperature_gradient

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There's another technology option, sat between A2A and A2W which is a hybrid of both which looks quite attractive if it takes off and becomes more widely available - Panasonic have a system called Aquaria Loop, intended for apartments/large buildings, which uses in-room W2A units (powered with their own integral heat pump) that can provide both heating and cooling, which are connected to the building's wet pipework system with an outdoor unit, which maintains the loop at something around room temperature, above dew point to prevent condensation.

I missed this @temperature_gradient . I wonder if any other manufacturer has this as an add-on..

 

Mitsubishi have something called HVRF, this is their VRF with 2 main CH pumps feeding multiple fan coil units with water but acting like an AC system, they heat and cool, we have installed several of these and I must admit it is some of the best tech I have seen in the cross over DX market. 

@ashp-bobba that's a different idea. Look at the Panasonic system to see what it does.

@djh ah, I have never seen this before, interesting idea, so a central ASHP but a much lower loop temp then a local top up with mini units in each room. I like Panasonic, they do great commercial gear, I got a 70kW ASHP to do at the end of the year using Panasonic.

It great being in an industry that is evolving thats for sure.

One more quick one. A local installer I contacted has just told me it could be 6 months before the BUS grant is available for air to air. Any idea what the hold up is?

Good questions @temperature_gradient. My understanding is...

1 Yes air to air can be used for whole home.

2 For small rooms it's common to use direct electric heating. 

4 Condensate water can go into surface drains and soakaways.

If you like YouTube there's some information on The EV Puzzle and Tim & Kat's Green Walk

And another question. How do defrost cycles work on air to air heat pumps? 

As I understand it an air to water system defrosts the outdoor heat exchanger by taking heat back from the heating water circuit. I presume air to air doesn't defrost by taking heat from the rooms. Am I right in thinking that means air to air systems take a bigger efficiency hit from defrosting?

@springswood, our podcast episode on A2As with @ashp-bobba drops on Wednesday afternoon, but we never got around to discussing the defrost process… @ashp-bobba can you please explain this when you get a moment.

Posted by: @springswood

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And another question. How do defrost cycles work on air to air heat pumps? 

As I understand it an air to water system defrosts the outdoor heat exchanger by taking heat back from the heating water circuit. I presume air to air doesn't defrost by taking heat from the rooms. Am I right in thinking that means air to air systems take a bigger efficiency hit from defrosting?

The defrost cycle on an A2A works almost the same as the A2W but where on A2W you need a volume of water to offset the energy needed to complete the defrost cycle without effecting the home to much, A2A kind of short cycles the refrigerant circuit by way of stopping or tuning the indoor fan to very low while it briefly cools the indoor coil, it can do both things with this fan and choose which it needs a different times it just works out whats the minimum heat it needs to take back. With an A2W its not so easy to stop all of the water flow and get away with it, so with A2W we look for a good body of water to exchange (open loop, bypass rad or volumiser) and allow the flow and in fact encourage the flow, with A2A we stop the flow in this case we stop the forced draft heat exchange or limit it, push that hot gas through the external coil and allow the defrost to take place. 

Basically both systems use the stored energy in the home to reverse back to the external coil for a short period to complete the defrost cycle.

Posted by: @springswood

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One more quick one. A local installer I contacted has just told me it could be 6 months before the BUS grant is available for air to air. Any idea what the hold up is?

We are being told that they are working through compliance issues and CPS processes (the lack of companies registered and the lack of CPS bodies able to cover A2A) 

Posted by: @springswood

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One more quick one. A local installer I contacted has just told me it could be 6 months before the BUS grant is available for air to air. Any idea what the hold up is?

I reached out to MCS directly last week on this and here's what they told me.

The hold-up is essentially a formal accreditation process. MCS's updated scheme documents are currently going through approval with UKAS, which they say should be completed soon. Once that's done, the Certification Bodies then have to go through their own separate UKAS process to gain accreditation to certify air-to-air installers, and that includes demonstrating they have the right competencies in-house to assess A2A installations properly. 

The answer from MCS is that they can't give a firm timeline because it depends on both UKAS and the individual Certification Bodies. Your installer's six-month estimate may well be in the right ballpark, but it's not a figure MCS will commit to.

In the meantime, MCS has been advising installers on what they need to do to prepare. The competency requirements are outlined on their website here if you or your installer want to get ahead of the process.

The problem with preparing is MCS need you to hold:- Refrigeration, Air Conditioning and Heat Pumps (RACHP) at Level 3 or equivalent to be the NTP but you only need NVQ lvl 2 and a couple of bolt on courses to be the NTP for air to water systems. The issue with the RACHP course is there are only around 10 centres in the UK that offer it and it is a 3 year course. most of us are floating around the older C&G certification with F-Gas Cat1, this has been the norm forever and is over 90% of the current market, unfortunately it now seems not good enough. 

They will need to come up with an experienced route assessment NVQ bolt on otherwise 90% of the industry won't care about the grant as its not enough to move industry to drive the centre's to teach this course and qualify the engineers to NVQ lvl3. I have been saying about this for 8 years but not in relation to the MCS part thats new. 

MCS aren't involved in commercial a2a installations which seem to work well, at least in my limited experience. Why do they need to be involved in domestic?  I presume it's linked to the grant but will that exceed the mcs overheads by enough to be worthwhile?

Please feel free not to answer that question.