Space Heating Options

[SteamyTea]

  On 24/01/2023 at 12:43, Gill said:

Hmm - and I though condensation would get worse as we seal up the house.

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It is a statistical 'thing'.

 

There is Absolute Humidity, the actual amount of water, by mass, whether as solid, liquid or vapour, in each cubic metre of air, then there is Relative Humidity, what we tend to talk about most as it is easier to measure and is the fraction, in percent, of the amount of water, as vapour, that can evaporate off a surface of water, into a cubic metre of air.  Sounds a bit complicated, but it takes air pressure into account and you may well he terms like vapour pressure and partial vapour pressure.  No need to worry about the terminology.

It is possible to calculate one from the other, but easier to use an online calculator.

What it basically comes down to is that even if you have extremely high external RH, once that is warmed a bit inside the house, the RH drops.

 

I am currently at 5.6°C external temperature and 90% RH, once that air has warmed up in the house, the same mass of water is still in the air (about 7 grammes/m³), but because the temperature is now 21°C, the RH is now 42%, which is probably too low for fungal spores to start sprouting.

 

So getting the place warmer will drop the RH, as long as it is not totally airtight, like a submarine.  It is why forced ventilation is used in airtight houses.  There is a lot of chat about CO₂ levels, but high internal RH is what will make you feel uncomfortable, and unless you are used to it, sleepy.  Think a Far Eastern holiday with 40°C and 99% RH, two drinks and it is tiring.  Never seen anyone sleeping out in the open in the Central Antarctic, the driest place on Earth.

 

 

 

[Gill]

  On 24/01/2023 at 13:56, SteamyTea said:

Think a Far Eastern holiday with 40°C and 99% RH, two drinks and it is tiring

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Three drinks and you're good to go...

[Nickfromwales]

  On 24/01/2023 at 15:55, Gill said:

 

Three drinks and you're good to go...

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He's good to go after half a shandy.

[SteamyTea]

  On 24/01/2023 at 17:12, Nickfromwales said:

He's good to go after half a shandy.

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After 1 drink I start to feel it, after 2, anyone can feel it.

[Jenki]

  On 24/01/2023 at 18:26, SteamyTea said:

After 1 drink I start to feel it, after 2, anyone can feel it.

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🙈🤣

[Gill]

Having done a fair bit of reading since starting that thread, I'm in the process of sourcing some estimates for putting in A2A system.  The published COP for Mitsubishi and Daiken models seem very appealing and I think will work well in our space and hopefully down the line when we look to solar, we can look to use the cooling capabilities too.  We'll keep the storage heaters until we've made it through a winter and have some real world performance data at lower temps.  If the A2A doesn't cut it, at least we'll have backup.

 

Revisiting this thread as I turn my attention to hot water.  I don't think i'm convinced on the ESHP for our particular situation.  Primary reason is it will be taking heat from the house which is currently expensive to heat and will probably continue to be for the next couple of years as we slowly modernise and tackle the heat losses.  We also have no alternative heat supply and no plans for stoves or wood burners which would seem to be a good match up for ESHP.   

 

As I mentioned back at the start, our current DHW through an immersion tank on the ground floor with two sizeable tanks in the attic.  Originally everything apart from the kitchen tap and the outside tap was fed off these.  Back when we moved in, I had both the toilets switched over to fill from mains which has rectified the slow and noisy fill .  

 

In an ideal world, i would like to get rid of of the attic water tanks and move any new system DHW system to the attic eves.  This would give us potential to create a habitable space in the attic and free up the space currently housing the immersion tank downstairs. 

 

I'm trying to understand if unvented cylinders and buffer tank (storage for when we get solar) would meet our needs and allow us to get rid of the water tanks.   I measured my water flow rate today from the outside tap (connected to mains) and we're getting 1 ltr every 2.5 seconds which I believe is considered good.  Not quite sure how water pressure fits into the picture but I suspect i'll need to get a gauge and measure that.   What other key things should I be taking into consideration ?  

 

 

[ReedRichards]

Even the best-insulated hot water tanks lose heat.  If they are inside the heated fabric of the building that lost heat goes towards heating the house so it's not wasted at times when you actually want to heat the house.  Heat lost from a tank in the eaves is just lost, although maybe not if the tank is relocated into a cupboard that forms part of your new habitable space.

 

 

[Gill]

  On 26/03/2023 at 18:15, ReedRichards said:

Even the best-insulated hot water tanks lose heat.  If they are inside the heated fabric of the building that lost heat goes towards heating the house so it's not wasted at times when you actually want to heat the house.  Heat lost from a tank in the eaves is just lost, although maybe not if the tank is relocated into a cupboard that forms part of your new habitable space.

 

 

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Good point. We have a cold attic and unless we do a full replacement roof it's going to be cold for a while. 

 

If we did put anything up there I would be insulating tanks and pipes as much as feasible. If we do ever make a habital space I'd be looking into warm roofs. 

 

Our old immersion tank does give off a little warmth but it's position means I can't get at it to insulate it more. Think I'd be willing to sacrifice the minimal gains we're getting at the moment. 

 

[ReedRichards]

If I were you I would put the new unvented cylinder where the old one is for now then relocate it when you make your loft into a habitable space.

[Gill]

Thanks - I'll need to work out how that would play out with solar and a a buffer tank. Don't think we'd have space for two tanks in the current location. Some basic maths tells me battery is not cost effective yet. 

[Iceverge]

Electric batteries are not worth it really unless you can do some serious load shifting from night to day. I.E work daily on high load computers from home. 

 

A 300l UVC is a superb heat battery. We bank 10kWh every day from cheap overnight electricity. 

 

From my experience doing calcs the absolute cheapest way to power a house is A2A for space heating and solar PV for with divert for water heating + E7 in winter. 

 

Just bought an A2A, waiting for it to be delivered. PV will come too at some stage. 

 

 

 

 

[joth]

  On 27/03/2023 at 00:05, Iceverge said:

the absolute cheapest way

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Just to clarify you're talking combination of capital and running costs based on some assumptions?

A2W (possibly extract air) heat pump for DHW (with PV+battery) will give lower running costs in absolute terms. And resistive heating will be cheaper in capital cost terms.

So selecting a mix of resistive + heat pump will depend on the assumptions around usage patterns and quality+size of property, and future energy prices, etc.

(Not saying it's a wrong or uncommon conclusion ,  just it will depend on circumstances and assumptions)

 

[Gone West]

  On 27/03/2023 at 00:05, Iceverge said:

absolute cheapest way to power a house is A2A for space heating

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Oil in our area has gone from 85.17p/l in January to 68.11p/l today, so a volatile market. At todays price, to match a 90% efficient oil boiler you would need a CoP of over 4 for the A2A HP, so it's close.

[Iceverge]

  On 27/03/2023 at 02:37, joth said:

Just to clarify you're talking combination of capital and running costs based on some assumptions?

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Yes. 

 

An ASHP at very low flow temps have good efficiencies but I don't think as good as an A2A and ESHP combo. 

 

Very much correct re the usage patterns. I am assuming a 25 year PV lifespan too. The trouble with heat pumps for water is they start to run out of COP as you approach usable DHW temp, negating much of their benefit.  PV + diverter doesn't care and will heat water from 10-20deg the same as 60-70deg. 

 

  On 27/03/2023 at 07:20, Gone West said:

Oil in our area has gone from 85.17p/l in January to 68.11p/l today, so a volatile market. At todays price, to match a 90% efficient oil boiler you would need a CoP of over 4 for the A2A HP, so it's close.

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Yikes, oil is certainly cheap. I didn't realise it was so much so now. 

 

From a carbon point of view I think a new oil boiler at 90% plus efficient isn't the worst way to use fossil fuels. A relatively better use of them than a 30% efficient car. 

 

Better still would be tackling some of the heat loss of the building although this isn't always readily achievable. 

 

 

Edited March 27, 2023 by Iceverge

[crispy_wafer]

  On 27/03/2023 at 08:02, Iceverge said:

An ASHP at very low flow temps have good efficiencies but I don't think as good as an A2A and ESHP combo

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Please can I ask what is an ESHP?  I feel that I'm missing some knowledge on something.

[Iceverge]

Exhaust source heat pump for DHW. 

 

https://www.vaillant.com/home/products/arostor-hot-water-heat-pump-10752.html

 

@Thedreamer has a Joule model. 

 

[SteamyTea]

  On 27/03/2023 at 08:21, crispy_wafer said:

Please can I ask what is an ESHP? 

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Exhaust air heat pump.

It is like a normal air to air heat pump, but extracts the air out of the building to heat water.

The problem is, the air in the building has to be heated, so can become very expensive if the heating is electrical resistance.

Some on here have used them to good effect though, especially if it is integrated with the ventilation system and DHW usage is relatively low, in proportion to the building volume.

DHW usage is really a function of occupancy, more people, more hot water used.

[billt]

  On 27/03/2023 at 08:27, SteamyTea said:

Exhaust air heat pump.

It is like a normal air to air heat pump, but extracts the air out of the building to heat water.

The problem is, the air in the building has to be heated, so can become very expensive if the heating is electrical resistance.

Some on here have used them to good effect though, especially if it is integrated with the ventilation system and DHW usage is relatively low, in proportion to the building volume.

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I think that you'ld normally have them ducted so the air comes from outside the building and returns to outside the building.

[SteamyTea]

  On 27/03/2023 at 08:50, billt said:

 

I think that you'ld normally have them ducted so the air comes from outside the building and returns to outside the building.

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Yes.  With a bit of imagination they can be effective.

If they cost the same as ten years electricity, about $1640 at my current inflated rate, I would consider one.

"Rich man sweating in a sauna bath, poor boy scrubbing in a tub"

"Me, I stay gritty up to my ears, sitting in a puddle of mud"

[crispy_wafer]

So...

 

if you add this to an ASHP A2W system rather than a normal cylinder, then you don't need to interrupt the space heating requirement for DHW generation. 

 

Each case is different I guess, but, as a rule is it better to separate the space heating system from the DHW system, or have them combined?  At < 2k for a 270l arostor they don't seem beyond the realms of affordability either.

[SteamyTea]

  On 27/03/2023 at 09:08, crispy_wafer said:

as a rule is it better to separate the space heating system from the DHW system, or have them combined

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My feeling is separate is better, Space Heating is at different times, at a different temperature and for a different purpose than DWH heating.

Bit like buying a RangeRover and hope that it can pull a plough occationally.

[JohnMo]

  On 27/03/2023 at 07:20, Gone West said:

90% efficient oil boiler

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Could you run it in the same low temp mode as a heat pump and over 100% efficiency through condensing?  Same as a gas boiler?

[ReedRichards]

What you can't do with most oil boilers is get them to modulate; they're either full-on or off.  

[Gone West]

  On 27/03/2023 at 11:21, JohnMo said:

Could you run it in the same low temp mode as a heat pump and over 100% efficiency through condensing?  Same as a gas boiler?

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No because IIRC Grant recommend a minimum return temperature of 50C which I think is to prevent corrosion.

[SimonD]

  On 27/03/2023 at 15:35, Gone West said:

No because IIRC Grant recommend a minimum return temperature of 50C which I think is to prevent corrosion.

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It's 40C for ufh on the Vortex exactly as you say to prevent corrosion of the water jacket. For normal rads they recommend 70/50.