While I struggle to find a sound consultant that can provide the necessary analysis, I'm beginning to spec the heating system I'd like to install.

Current requirements:

1. Single outdoor unit (better cost/benefit than multiple units + easier to get permission, but louder and slightly lower COPs than two smaller units)

2. SCOP of 4+ (to cut CO2 by 40%, and heating costs by 25%, vs. my high efficiency combi boiler). Ideally, I’d like an official SCOP of nearer 5, as I apply a 20% haircut to official figures, but I’d need an R32 system and suitable ones aren’t available yet. Maybe by the time planning comes through…

3. Circa £2k for equipment (including ducting etc. if necessary)

4. 10kW max output

5. Heat distribution to three zones (had hoped that one central zone would suffice, with heat flowing to other rooms naturally, but don’t think it would work)

Point 4 is taxing me. Which would be better, a single internal unit ducted to three zones or a multi split system with three internal units? I -think- the latter, as:

1. Running the narrow pipework to each zone would be a lot easier than installing outward and return ducting between each zone and a single central unit, plus thermostats for each zone.
2. The wall mounted units will mix the warm air in faster and better than air delivered through a duct.

A single indoor unit is cheaper than three indoor units, but I think the hassle and cost of ducting, plus the less efficient air mixing, offsets the benefits.

Would appreciate any thoughts on this issue, and any others please.

Posted By: GarethC1. Running the narrow pipework to each zone would be a lot easier than installing outward and return ducting between each zone and a single central unit, plus thermostats for each zone.

In general, you duct the individual supplies, but not necessarily all the returns - so long as there is a path in the general zone to the return duct you're good to go - just have to make sure the return openings are large enough for the overall airflow. I suspect there isn't much experience of ducted systems in the UK, though. For your point 4, 10kW isn't huge (would be known as a "3 ton" system over here) and so is easily within the capabilities of a single unit. The fewer units, the fewer things to go wrong (IMHO).

Your only challenge is running the ducts - over here, most places have basements / crawl spaces where the ducts can be run, or you can use "micro ducts" - though there can be noise issues with the latter if not designed properly.

Paul in Montreal.

Posted By: owlmanI thought most of the Air to Air units here in the UK used copper microbore between the heat pump and the fan emitters in the rooms. At least the ones I'm looking at do, what is the talk of ducts, have I missed something?

Mini/multi "split" systems use copper to transfer refrigerant to the local heat exchangers. Single units have one indoor and one outdoor unit - the outdoor is the evaporator and the indoor is the condenser and then a fan blows over that and you distribute the heated air via ducts. If your units are reversible, then in A/C mode the outdoor one becomes the condenser and the indoor the evaporator. The compressor is always in the outdoor unit.

Paul in Montreal.

I'm currently designing a multi split system that will use individual ducting to supply each room and extract from kitchen and bathrooms.

I figure that if designed correctly and the equipment is of decent enough quality than it should be quieter than having a condenser mounted in each room. they are a bit ugly and quite noisy too.

The condenser will be installed in the false ceiling above the stair landing that accesses each room so that the ducting runs will probably be less than 2 meters each. The ducts drawing air out of the bathroom and kitchen will be a bit longer.

In France you can buy the multi split as a kit that is p-assembled and charged with the refrigerant ready to go.

GarethC, the following PDF has a layout diagram of the parts available in a typical system. Its in French but you should still find it useful and be able to get an idea from looking at the images.
Ask if you want any further info.

http://s2.lmcdn.fr/multimedia/791400011044/1597d6d557edd58/produits/mode-d-emploi-vmc-double-flux-moyen-rendement-equation-1.pdf

Ive been reading that r32 is flammable and produces hydrogen flouride, highly toxic. No thanks

This is one of the documents I read (which includes looking at R32 multi-splits in a domestic environment). A bit hard work... But the Japanese should have the best results. They've been on sale in Japan for a few years now, and the Japanese are most concerned with safety as, due to the prevalence of earthquakes, leakages from systems such as this are a much greater risk than they would be in the UK.

This does consider HF. Haven't had time to read any conclusions yet.

http://www.jsrae.or.jp/committee/binensei/2013PR_e_ab.pdf

I think there is research that suggests and which is ignored in the "industry spin" research, that there is a possible issue when r32 is mixed with the hvac lubrication system oil.

Whoops. Forgot links.

R32 has finally made it's way to non-premium A2A in the UK. Another step along the long road towards me actually installing something (although impending self imposed unemployment may mean yet another delay).

I'm looking at FTXM-M units. See top of page 17 of this: http://tinyurl.com/h7mrtja for spec, and compare to the middle of page 18 to compare with equivalent R-410A units (FTXS-K). Essentially, R32 offers about a 6% improvement in SCOP performance, which is not to be sniffed at. The ones I'm looking at have claimed SCOPs of 5.1 (vs. 4.8 for R-410A equivalents), giving me more confidence of reaching my target of at least 4.0.

I'm looking at three of the smallest units rated 2.5kW for heating (max 4kW) and a couple rated 4kW (max 5.2) for a larger rooms. Individually they're pretty good value. The former are about £600 each including the outside unit here http://www.daikinonline.co.uk/daikin-ftxm-rxm-inverter-r32.html.

But of course I can't really have five outside units, so intend to have two multi-splits, one with three emitters and one with two. All in the kit comes to £3k. I hope I'll get a discount on that, but will still have to buy pipes and other gubbins, so the total will probably be about that. Not too bad though.

I think one will serve the lounge and children's bedroom, and the other will do the kitchen, our bedroom and the spare bedroom. My reasoning is that heat pumps perform better when not maxed out. If I had one which did lounge and kitchen, which are warmer rooms used at similar times, and another which did the bedrooms, to an extent there would be more times when one was working flat out, less efficiently, and the other idle.

Does that make sense?

In fact, does anyone know the methodology used to measure multi-split performance? I can't find details on the inter-web. Generally, the stated SCOPs for multi-splits are lower than for otherwise equivalent individual split units, but I don't fully understand why. I suspect the multi-split performance will vary greatly depending upon how it's used, and I'd like to get close to what single splits to achieve.

The GWP of R32 is 675, less than half that of the R410a in my heatpumps, so a big improvement, but I think it's a pity they didn't have the courage to approve propane (R290) , especially for smaller installations, as its GWP is only 3.3