Split Air con

[b0rn2sk8]

Surely this is going to depend entirely on how it's powered and what kind of tariff you're on? If the heat pump is 300% efficient while heating at moderate outdoor temperatures, then your electricity unit cost needs to be less than 3x the gas unit cost - I don't see how that's the case on most tariffs these days unless you're on something like Agile and can be selective about when you run it. SVR for gas is around 6.5p, electricity is around 25p, meaning the heat pump will need to be 385% efficient just to match running cost.

You are comparing applies with oranges because you are not factoring in the efficiency of the boiler.

In the sorts of weather we get (like today), the heat pump could be closer to, if not exceeding 400% efficiency, particularly if the poster is using it on low fan speed (low power) to a sensible temperature.

The gas boiler isn’t 100% efficient, it may be rated to 96% but it just isn’t in the real world. It wouldn’t even get up into the 90’s without a full weather compensation set up with flow temperatures well under 50C.

The vast majority of gas boilers are operating in the low 80’s, even modern ones, because they are not configured for efficiency.

If you are heating a single room with a gas boiler it will probably be down in the 50% range because it will be cycling like mad.

 

[Vertigo]

In the sorts of weather we get (like today), the heat pump could be closer to, if not exceeding 400% efficiency, particularly if the poster is using it on low fan speed (low power) to a sensible temperature.

I don't pretend to understand how it all works but the outside unit is rated at up to 4.3kW of heating/cooling power but has a maximum power consumption of 0.98kW which presumably equates to over 400% efficiency at the theoetical max.

 

[b0rn2sk8]

I don't pretend to understand how it all works but the outside unit is rated at up to 4.3kW of heating/cooling power but has a maximum power consumption of 0.98kW which presumably equates to over 400% efficiency at the theoetical max.

Correct but as it gets colder/warmer, the maximum output it can heat/cool will reduce for the same power input. So while that’s the max, when you really need the heating say 5C outside, it will be a bit less efficient than when it’s 12C outside like today.

 

[Vertigo]

Correct but as it gets colder/warmer, the maximum output it can heat/cool will reduce for the same power input. So while that’s the max, when you really need the heating say 5C outside, it will be a bit less efficient than when it’s 12C outside like today.

Yeah, makes sense that it'd have to work a bit harder to suck energy out of the outside air when it's colder. Is there any harm in running it when it gets very cold outside? Tbh on the days when it's like 0C outside, I've refrained from using it, although generally that's cold enough that I want the central heating on anyway, lest the house freezes.

 

[b0rn2sk8]

Yeah, makes sense that it'd have to work a bit harder to suck energy out of the outside air when it's colder. Is there any harm in running it when it gets very cold outside? Tbh on the days when it's like 0C outside, I've refrained from using it, although generally that's cold enough that I want the central heating on anyway, lest the house freezes.

No, its fine, use away at your leisure.

 

[squerble]

I did try a search but kept failing so... has anyone had their heating entirely replaced with an air-to-air system?

Given the upcoming relaxation of the rules allowing air-to-air heat pumps that offer cooling to be installed, I'm hoping this means that these systems will be available via the BUS (i.e., included for the £7500 grant). If so, this would give us quite an opportunity to go air-to-air for the whole house. It'd be quite interesting to weigh up the cost of such a system (plus us having to get some kind of hot water tank installed). If it comes anywhere close to us switching to an air-to-water heat pump system, I don't see why anyone would go for that as you'd be able to get a fully heated and cooled house for not a lot of money.

For us to do the whole house though, we'd need to get a loft unit with five/six output ducts for upstairs, plus three wall units for the three main downstairs rooms, hence me hoping someone has done something similar!

 

[Reuben klang]

I did try a search but kept failing so... has anyone had their heating entirely replaced with an air-to-air system?

Given the upcoming relaxation of the rules allowing air-to-air heat pumps that offer cooling to be installed, I'm hoping this means that these systems will be available via the BUS (i.e., included for the £7500 grant). If so, this would give us quite an opportunity to go air-to-air for the whole house. It'd be quite interesting to weigh up the cost of such a system (plus us having to get some kind of hot water tank installed). If it comes anywhere close to us switching to an air-to-water heat pump system, I don't see why anyone would go for that as you'd be able to get a fully heated and cooled house for not a lot of money.

For us to do the whole house though, we'd need to get a loft unit with five/six output ducts for upstairs, plus three wall units for the three main downstairs rooms, hence me hoping someone has done something similar!

Me. I’m in the trade through. I didn’t think it would be so soon before people started doing it. I was speaking to a chippy the other day, he was asking me and basically said everyone he spoke to (plumber, heating eningeer and sparky) all said they’re a waste of time. It’s mainly down to people not realising they do heating.

You should see my garden, I have 4 outdoor units. All mitsubishi electric. I’ve ASHP solely doing my hot water.

Most of the experts if you will say that set up is the future. The lad who does the daikin altherma course was talking about it during the hybrid system (gas and electric) saying that with new builds not having gas and being insulated to the high heavens and almost if not air tights and requiring a heat recovery vent systems. The houses are absolutely boiling in the summer and basically forcing people into getting A/C for the summer because the houses retain too much heat.

Rather than having both systems with one being retrofitted a year or two down the line - which can do both heating and cooling. Just do away with ugly rads and install A/C from the get go.

Having said that underfloor heating is amazing, you could have the heating loop just running at <20°c for underfloor all year round and it’ll just take that chill off the floor during the winter and the A/C does the air temp.

 

[squerble]

Me. I’m in the trade through. I didn’t think it would be so soon before people started doing it. I was speaking to a chippy the other day, he was asking me and basically said everyone he spoke to (plumber, heating eningeer and sparky) all said they’re a waste of time. It’s mainly down to people not realising they do heating.

You should see my garden, I have 4 outdoor units. All mitsubishi electric. I’ve ASHP solely doing my hot water.

Most of the experts if you will say that set up is the future. The lad who does the daikin altherma course was talking about it during the hybrid system (gas and electric) saying that with new builds not having gas and being insulated to the high heavens and almost if not air tights and requiring a heat recovery vent systems. The houses are absolutely boiling in the summer and basically forcing people into getting A/C for the summer because the houses retain too much heat.

Rather than having both systems with one being retrofitted a year or two down the line - which can do both heating and cooling. Just do away with ugly rads and install A/C from the get go.

Having said that underfloor heating is amazing, you could have the heating loop just running at <20°c for underfloor all year round and it’ll just take that chill off the floor during the winter and the A/C does the air temp.

I'd honestly love to convert the house to a central air system, just run ducts between studs down the walls, and have one/two big loft units doing everything. Our heat loss estimates are usually around 3.0-3.5kW at -3ºC outside, which is around 10k-12k BTU, so not a huge deal even for even a single loft unit. I've got an Octopus guy out to do a proper heat survey in January so I should get a much better number then.


Our "lottery dream house" is basically: something that is close to, if not, passivhaus; fully ducted heating and A/C system run by heat pump with the units either in the loft, or even have a basement (if that's possible); proper recessed windows with shuttering system to keep sunlight out in summer; a full MVHR system which means we can have windows without trickle vents, because they're just awful; and, of course, a full solar + battery system.

 

[happy_2008]

Boiler was spewing out water when we got back from holiday yesterday so no central heating or hot water, luckily i remembered the air con units have heating function