Split Air con

Thanks to this thread popping up again, finally remembered to re-contact the guy who fitted our wall based lounge unit last year, so we can work out a plan for the two bedrooms and home office upstairs we want aircon in too.
Current plan is a ducted system in the loft to all three rooms, with closable vents so we can turn off individual rooms if we wish.
I wondered whether they would need an inlet vent from one of the rooms too (after all, you don't want it sucking musty loft air into the rooms) but he reckons a fresh air feed from outside instead is easier.
 
That's a very interesting question. Over winter, just out of interest, we ran our lounge one as a heater one day. The reading on the smart meter was not as high as I had expected it to be, and it warmed the room extremely quickly.
 
It seems about par gas to electricity wise i've found, it seems to use about 1/4 to 1/5 of the energy (depends a bit on outside temp) but obviously the price is about 4.5 times higher!
 
It's fairly easy to calculate out yourself. Just divide the electricity cost by the cost of your gas for each kw. So in my case for british gas in April you'd do 27.358p/7.280p = 3.76. So you'd need the electricity to provide 3.76x the heat per kw to provide the same heat as gas given equal spend. This figure can be directly compared against a figure commonly referred to in heat pump systems as "COP". Most heat pumps/air conditioners have a COP of around 3 so it'd only make sense to use that system for heating if the COP of your machine is around or higher that the calculated figure we did.

There is one caveat though, not all the gas you pay for heats your house, so you could multiple your gas price by say 10% to account for boiler inefficiencies, this gives up a value of 3.41. Given how most heat/air conditions have a COP of between 3-3.5, which is within what we calculated of 3.41 its as SoliD said, they are roughly on par based on Aprils prices.
 
bazzabear said:
That's a very interesting question. Over winter, just out of interest, we ran our lounge one as a heater one day. The reading on the smart meter was not as high as I had expected it to be, and it warmed the room extremely quickly.
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I'm definitely wondering if doing a large split system (I'd want a cartridge in each main room) would outweigh losing out on the ASHP grant vs. being able to have both heat and air conditioning for the whole house.
 
squerble said:
I'm definitely wondering if doing a large split system (I'd want a cartridge in each main room) would outweigh losing out on the ASHP grant vs. being able to have both heat and air conditioning for the whole house.
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In my head yes, I got a split system installed for all of upstairs, plus two wall units for £5.5k iirc, heat pump systems were coming in at 2.5x that after the grant.
 
squerble said:
I'm definitely wondering if doing a large split system (I'd want a cartridge in each main room) would outweigh losing out on the ASHP grant vs. being able to have both heat and air conditioning for the whole house.
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It's certainly tempting to find out. When our 3rd is fitted we would only need gas for water and cooking. "Blown air" seems to circulate at least as well as "static convection". Obv. I am not an expert in brownian motion etc!
 
Switching the house heating to a split system is easy to understand in principal. However it then leaves the question of what to do with hot water. The house is a 2017 build so is combi boiler/hot water on demand. I guess we'd have to switch to a tank system which would be immersion heater only. This would be a huge energy hit as well as needing to re-plumb the house to accommodate that. On the plus side, if we were to get solar then we could trickle feed the immersion so have "free" hot water during summer and other sunny days.
 
I just checked the RHI calculator for our new house and I'd only get £2,200 towards an install. When several websites are saying an air-to-water heat pump system will be anywhere from £8,000-20,000 for an install, the idea of going for a split system instead is very tempting.

I don't know if the ASHP system cost includes adding in a water tank and all the plumbing associated with it, which could tip the cost in favour of the ASHP, but I feel the added bonus of AC for the hottest of summer days (or just dehumidifying when drying clothes etc) would be worth it regardless...
 
squerble said:
I just checked the RHI calculator for our new house and I'd only get £2,200 towards an install. When several websites are saying an air-to-water heat pump system will be anywhere from £8,000-20,000 for an install, the idea of going for a split system instead is very tempting.

I don't know if the ASHP system cost includes adding in a water tank and all the plumbing associated with it, which could tip the cost in favour of the ASHP, but I feel the added bonus of AC for the hottest of summer days (or just dehumidifying when drying clothes etc) would be worth it regardless...
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Typically, that cost does include most the work needed (rads/pipe/tank). Very few properties have rads sized for the reduced temperature of ASHPs, also because of lower system temps you generally need higher flow so in the case of many new builds and 10mm microbore that’s everywhere. UFH is good if you have that with heat pumps. I think in either system you need immersion at some point to raise to 60c for legionella’s in the tanks.

From a cost perspective if you already have gas and your system/house is pretty new and efficient it doesn't really matter which system you use since you are buying from the grid. The consumption cost per kWh of heat in the building will be about the same for both systems at todays prices. You should be thinking about it the other way around. If you are buying more split units to be cool in the summer and use it for dehumidifying, then you get the added benefit of choosing to use electric or gas to heat at winter. Choosing a split unit for the primary purpose of heating is going to be more expensive than simply using your existing gas system given you don't generate your own electric and have access to cheaper gas.
 
Gammawolf said:
Typically, that cost does include most the work needed (rads/pipe/tank). Very few properties have rads sized for the reduced temperature of ASHPs, also because of lower system temps you generally need higher flow so in the case of many new builds and 10mm microbore that’s everywhere. UFH is good if you have that with heat pumps. I think in either system you need immersion at some point to raise to 60c for legionella’s in the tanks.

From a cost perspective if you already have gas and your system/house is pretty new and efficient it doesn't really matter which system you use since you are buying from the grid. The consumption cost per kWh of heat in the building will be about the same for both systems at todays prices. You should be thinking about it the other way around. If you are buying more split units to be cool in the summer and use it for dehumidifying, then you get the added benefit of choosing to use electric or gas to heat at winter. Choosing a split unit for the primary purpose of heating is going to be more expensive than simply using your existing gas system given you don't generate your own electric and have access to cheaper gas.
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Yea, I was weighing up how a split system could compare to the work of ASHP. The house is 2017 so quite modern with plenty of insulation so should be "cheap" to run. The future idea would be to replace the boiler with a split system that does all of the heating and cooling, plus a tank with immersion heater to heat the hot water (which could be trickle charged with a solar install, also in the future). More just getting the grand plan together for the next decade of the house :)
 
Well. Our plans for a ducted loft system to three bedrooms seems to have gone for a burton.
Our fitter has done some more research on what would be needed, and reckons larger units to make up for the heat in the loft, inlet and outlet vents to each room, and a separate unit for each bedroom would be required to do the job properly. Resulting in a much higher price that we'd originally planned for - £4,500 for just the parts, and probably 5 days of labour.

Three wall units (fed from a single outside unit) would half the cost.

There were two main reasons for avoiding wall mounted - the aethetics, and the worry about needing a condensate pump and the noise that would add. Neither of the bedrooms has a suitable outside wall for mounting the unit, so the condensate pipe would have to go up from the unit and along the top of the wall to outside.

But to half the overall cost, maybe we can deal with both those issues!

The other option is ceiling cassettes. So he's going to look into them too. I presume that would still leave them needing a pump for the condensate though. And I think they also are going to be less efficient like the ducted system, because the body of the unit is in the hot loft.
 
We have condensate pumps and don't really notice when they run.

I went through the same process as you, and the cost of a motorised valve damper assembly so we could control each room independently, loss of loft space and extra cost put us off.
 
bazzabear said:
Well. Our plans for a ducted loft system to three bedrooms seems to have gone for a burton.
Our fitter has done some more research on what would be needed, and reckons larger units to make up for the heat in the loft, inlet and outlet vents to each room, and a separate unit for each bedroom would be required to do the job properly. Resulting in a much higher price that we'd originally planned for - £4,500 for just the parts, and probably 5 days of labour.

Three wall units (fed from a single outside unit) would half the cost.

There were two main reasons for avoiding wall mounted - the aethetics, and the worry about needing a condensate pump and the noise that would add. Neither of the bedrooms has a suitable outside wall for mounting the unit, so the condensate pipe would have to go up from the unit and along the top of the wall to outside.

But to half the overall cost, maybe we can deal with both those issues!

The other option is ceiling cassettes. So he's going to look into them too. I presume that would still leave them needing a pump for the condensate though. And I think they also are going to be less efficient like the ducted system, because the body of the unit is in the hot loft.
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I have one large unit in the loft that is then ducted to 4 bedrooms with 3 inlets, but sounds like he wants to put 3 individual units in the loft, although not sure why the heat in the loft matters much as the system would be sealed?

Why the need to individually control rooms?
 
Our intention was a single unit as you have. He's taken advice from a colleague who has fitted a lot of ducted systems to houses (he has fitted a lot, but only to offices) who shared all these suggestions.

So the reason for changing from one big unit to three separates isn't to get individual control, it's because of the suggestion that the unit would be worked too hard to cool three distant rooms well. With the unit itself in a potentially very hot place (yes it's sealed, but if the unit itself gets super hot, then it must have an effect), and long stretches of ducting which can also take in heat, and reduces the efficacy of the airflow. He was reckoning ducted units in a loft are around 30% less efficient / effective than a split wall unit.

But I'd love to hear more about your set-up. There's nothing to say this guy advising him knows everything!
 
bazzabear said:
Our intention was a single unit as you have. He's taken advice from a colleague who has fitted a lot of ducted systems to houses (he has fitted a lot, but only to offices) who shared all these suggestions.

So the reason for changing from one big unit to three separates isn't to get individual control, it's because of the suggestion that the unit would be worked too hard to cool three distant rooms well. With the unit itself in a potentially very hot place (yes it's sealed, but if the unit itself gets super hot, then it must have an effect), and long stretches of ducting which can also take in heat, and reduces the efficacy of the airflow. He was reckoning ducted units in a loft are around 30% less efficient / effective than a split wall unit.

But I'd love to hear more about your set-up. There's nothing to say this guy advising him knows everything!
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Surely if that was the case then single big ducted systems would never have been created.

Mine is 4 bedrooms ducted unit, mitsubishi electric. Unit in the loft is pretty much smack bang in the middle of the house, so the Longest run is probably 5m. All outlets have insulated pipework, 3 inlets 2 in the bedrooms and 1 in the hallway. This is then connected to a large 7.2kw unit outside which also powers a wall unit in the lounge.

I had numerous quotes and all suggested the single unit for upstairs with one wall unit downstairs for the lounge. No one suggested separate loft units. I'd definitely get a second opinion.

I've only had mine installed since last October but when heating my very poorly insulated house it has never once struggled. These units are designed for much hotter climates than the UK, so it seems a bit mad to have to be so overkill.
 
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