Beelbeebub

Quick estimate, ignoring standing charges etc. Assume Gas 7pkwh Elec 28pkwh So break even SCoP is about 4. Fairly hard to achieve. Annual Gas usage 12,000kwh Annual elec Usage 4,000kwh Annual Gas cost £840 Annual elec cost £1,120 Total £1,960 Green tax on gas is 5% ie £168 Green tax on elec is 20% ie £224 If we swap the elec taxes to gas Gas £1,064 Elec £896 Unit cost is now 9pkwh for gas and 22pkwh (rounded in favour of elec). Now the break even SCoP is now 2.4, much easier to achieve. Most properties could achieve that with a very mild upgrade to emitters.

Realistically the only way to make people switch is to make it the cheaper option. The upfront cost can be dealt with via install subsidies, though that does just encourage the install price to remain high. The bigger issue is the cost of running the HP. This is a common point brought up by the anti brigade. The government need to make HPs the cheaper option. Then people will be kicking the door down to install them. One issue is the green taxes on electicty Vs gas. About 15-20% of the elec bill is green taxes, less than 5% for gas. If you shifted the taxes over in a moremormlessncowt neutral way, then the average bill of a dual user would stay the same, only the proportion spent on each fuel would change. But the elec only user would see a fall in costs and the break even SCoP for HPs where they cost less than a gas boiler would fall making HPs more attractive.

Actually seems pretty good. Will be better than break even (carbon wise) than burning gas in a CCGT station allmthe way down to -5C, which is fairly rare in this country. Even at -7C it puts out 2kw, enough for most rooms even with fairly minimal insulation and though the cop is fairly rubbish it's still 2:1, which isnvery useful vs electric.

As a follow up, I asked the supplier for some info on the lower temp performance of the units as the literature only specs at 7C external area. Anyway they got back to me (fair play) with ... Low Ambient Heating Performance Ambient Temp. RH humidity Heating capacity in average (W) Power Input (W) COP 0 70% 2560 821 3.12 -5 70% 2477 924 2.68 -7 70% 1862 947 1.97

That heat requirement is very low, and probably mostly hot water. Presumably there is a bigish unit inside for the GSHP? Probably near the back door (boot room?). Maybe the hot water cylinder next to it? This might be a bit out there, but what about one of those integrated heatpump water cylinders? It's an unvented water cylinder heated by a little air source heatpump sat on top fed by two ducts, usually about 180mm. That could replace your water cylinder or GSHP as long as there was relatively easy access route the two ducts outside. So that would take care of hot water The slightly funky bit would be rigging up some way of powering your UFH from that setup. If the cylinder had a secondary loop you could power your UFH from that via a heat exchanger? A bit out there, but it would remove the need for an external unit Edit: Just reread the OP, I misinterpreted 3,000kwh/year as the output no the consumption. So maybe too much for my suggestion

Yes, too early in the morning!

I think so. My guess is that vailant are a boiler company so that thinking is sort of built in to how they view things, and the (electrical) energy consumed by a boiler is not really relevant to the final heat output.

Or simply cop=yield+1

Good point about the mice. We are 5 floors up in an attic, but the little blighters do get about.....

I know everyone says "don't use speedfit/Hepco plastic pipe because it restricts the flow, use copper" But if I was going to use 22mm copper for the primary feeds, what about using 28mm plastic. The internal diameter of the 28mm plastic is a little bit more than the 22mm copper. 22mm copper is about the same per meter as 28mm plastic but I may have some long and difficult to access routes where pulling though a (pre insulated) length is pipe is easier than jointing then insulating 3m lengths in somewhat awkward conditions. Any thoughts? Should add, I was planning on doing the final runs off the primary in copper, 15 or 22mm to suit. This is just for a run from the unit outside through a loft space and possibly down a stairwell.

Which is why mixers should only be installed as a last resort. The only reason to have a mixer is having two zones that need to run simultaneously and one is significantly higher temp than the other. The classic example being UFH downstairs and Rads upstairs. Hence my musings about multiplexing.... does it allow for "seamless" switching between the flow temps? I seem to remember someone saying their HP would stop and then restart at the changeover. If it simply ramped up or down then it might work. You could mod your current setup by fitting a 2 port valve on both the rad and ufh loops (or a 3 port depending on your pipework). Then setting your blending valve to be the maximum safe temp. In UFH mode, the low temp is output, the valve to the UFH is opened and the pump is turned on (this bit is optional, might not be needed). The blending valve will go 100% hot trying to achieve it's set temp which is lower than the flow temp so you will effectively have an open loop. When you switch to Rads, the UFH loop is closed off and the rads opened. Just kicking ideas around! not actual advice!

I'e be really interested if it was possible for HPs to time multiplex output temps for two zones (UFH and rads). If the system simply switched output temps setpoints in synchronization with a 3port (or 2x 2port) valves that diverted between the two zones I don't see a technical reason why it wouldn't be possible efficiently. I also wonder if you could do defrost cycles by switching to DHW coil. As long as you had a bottom biased coil, you would steal a few degrees from the probably already cold bit of the dhw tank. You would then replenish the heat as the last part of the defrost cycle as you rampee back up to temp.

Yes, you would need a direct UFH mainfold without the mixer and pump or at least a minimum sized always on zone

Agreed, but I don't think the minimum volumes are as high as people think. Irrc grant/Chofu are happy with a 30l volumizer regardless of the size of the rest of the system, which implies the min volume is around 30-40l. 15mm UFH pipe laid at 200mm centers is about ½liter per m2 So a small house with a 60m² footprint and UFH only on the ground floor would be nearly 30l before you look at upstairs rads, primary pipework etc. Unless it's a very thin system, UFH adds considerable thermal mass as well

but also more water volume for defrost so less need for a volumiser!

We had a high pitched wail, loud enough to be clearly heard inside behind double glazing, from a nearby school boiler (actually the blending valve) for about 3 years. It was loud enough to be annoying to people living 200m away. Initially it was whenever the heating was on - so almost constantly over the depths of winter. They progressively managed to reduce it until by the 3rd winter is was a "honk" when the system started up. They seem to have finally sorted it as it's been quiet since. But the fan exhaust is clearly audible outside when it's going full blast.

Is there much of a downside to having too much UFH pipe? The capital cost is fairly negligible.

I'm shocked the Telegraph would twist the facts to suit it's agenda Shocked!

Exactly, unrealistic noise requirements are a defacto ban. Maybe you should set up a speaker and run it with white noise at the noise level the HP will generate and see is anyone complains. Then when the planning objection is "it will be too noisy and disturb people" you can say "it hasn't yetx 😁

I think there is a public perception they are noisy. Maybe they are refering to objections to planning that cited noise concerns? Noise is almost always mentioned, along with they don't work when it's cold. There are aspects of the "culture war' bleeding into this. A well know YT building channel is not keen on them and recently visited a terrible install that was making a racket. It was down to a failed bearing due to poor installation and maintenance and was obviously not the normal noise. Yet he did a YT short "people tell me heat pumps arent noisy! Well listen to this!". And underneathg5the fist comment was about HPs being for "the woke". It's almost like the Trump supporters proudly tuning their trucks so the can be "rolling coal to own the libs"

Lifting the size restrictions would help with noise reduction. Getting rid of the boundary requirements is also sensible. Maybe some sort of scheme where the noise aspects are waived if the unit has a pre-approved certification. That would involve testing the units in a set of scenarios (including worst case situations with reflective surfaces) so it can be deemed to be acceptable in any installation. If a HP only punts out 35db at full chat then it can't really be an unreasonable nuisance.

I think this is important. I think historically alot of installations have defaulted to a large 4 port buffer to prevent the installer having to think too hard about the rest of the system. Whilst it does allow the HP to run even if you balls up the other side of the system the cost is the system will run inefficiently in all but perfectly balanced conditions - and if you can achieve those regularly, why bother with a buffer?

You can usually unzone UFH fairly easily by unclipping the actuators (normally on return). The zones are then always on. You can adjust the heating to each room by tweaking the flow rate. I unzoned my house (admittedly fairly open plan) and the UFH runs much better. Also a ceiling fan works well to move the warm air down to ground level. We havea 4.5m high lounge with a mezzanine. When we ran the wood burner we would hit 28C upstairs and 23 on the sofa. Now we turn the fan on and downstairs gets warmer immediately

It does need to be made clearer that "more efficient" doesn't necessarily mean "cheaper". Unless you HP install is terrible (and historically some have been) you will almost always be ahead in terms of carbon emissions. If your first priority is dropping those, then a HP will do that. But in order to actually be cheaper, especially with the higher up front cost of a HP, then your install does have to better than has perhaps been typical in the industry.

Most* monoblock HPs have a pretty powerful built in pump. For example the grant/chofu HPs have 10m or 12m head. It's unlikely he will need a additional pump, those are only needed for very big and complex systems. In fact if he has UFH fitted downstairs he may need to remove that pump and run direct. Historically, installers have often put big hydraulic buffer tanks in, which do need additional pumps, but the thinking now is to run the systems with a few "bells and whistles" as possible. The ideal is a single 3 port valve and no zoning. If (big if) his heating system was designed with a 55C flow temp, which was recommended in 2019 but not an actual requirement then the HP should be able to run at about 45C to give a similar output on those rads (the mean flow temp of a radiator spec'd for a boiler flow temp of 55C is 45C because they have DT of 20C across the rads. A HP has a smaller DT of about 5C so will have a Flow temp of 47.5C for the same mean rad temp of 45C) One test would be to turn his boiler flow temp down to 55C (or lower) and see how he goes. If his house is nice and warm with a 55C or lower flow temp, then he probably doesn't need any significant changes to his heating system. *I believe the Samsung Gen6 monoblocks use an external, customer supplied, pump.