Just Starting

[Rafiki]

First Post on here from a new member just introducing themselves.

We are  building  an off grid house ( no services near enough to connect) on a family farm in North Bucks.  Timber Frame supplied by Border Oak. Ground works "should" start next  month after almost two years to get full PP.

[Iceverge]

Welcome and congrats. 

 

Surely electricity is available in Buckinghamshire?

 

You'll be running a Genny otherwise mid winter or hand washing your clothes. 

[SteamyTea]

Welcome.

Isn't North Bucks Milton Keynes.

Just kidding, I know the area reasonably well.

[ToughButterCup]

Hello - welcome.

I bet you are fizzing with anticipation: remember that. Hold on to it like was a cherished family member about to fall off a -  summat or other. Because you'll need to hold on to that memory for (potentially) quite a while. Lets hope not though.

 

The bit of your post that will have hooked more than one or two on this board is

Quote

We are  building  an off grid house ( no services near enough to connect)

 

And, given that collectively we are more nosey than a herd of under-fed tomcats we need plans, site plans, M+E design, poo tank details, pv design, photos - anything ..... please😁

 

Pop your ideas into the relevant subsection of the board, that'll  release any inhibitions the BH Commentariat may have had.  Cos we like other people's problems more than our own.

 

Helps us treat our own procrastination better when we try to solve others' problems.😏

[Kelvin]

Awesome. Off grid in Bucks. Wow! Be keen to see your scheme to power the house. 

[Rafiki]

Nearest electricity pylons are  about 500 metres away. The cost of getting connected to the National Grid far exceeds the cost of a large PV array, large Lithium battery bank sufficient for 3 days and a generator. In the Summer months there will be enough electricity to heat the water by immersion, provide all house needs ( gas hob and kettle, via propane tanks) run an EV and have A/C if we wanted. In the Winter electricity generation is much lower and water heating ands UFH will be provided by a log burner. The diesel generator may have to operate 150 to 250 hours a year, primarily in the winter. We will do all the plumbing for a  propane boiler as a back up but only buy and install it, if in the first winter it is neccessary.

Central to the Heating and DHW is a Thermal Store of at least 300 litres which enables up to 4 means of heating the store and up to 3 means of using the heat therein - all houses should have one.

We are fortunate in having large agricultural barns for installing PV and the cost of PV panels ha some down a lot.

[jack]

16 minutes ago, Rafiki said:

Nearest electricity pylons are  about 500 metres away. The cost of getting connected to the National Grid far exceeds the cost of a large PV array, large Lithium battery bank sufficient for 3 days and a generator. In the Summer months there will be enough electricity to heat the water by immersion, provide all house needs ( gas hob and kettle, via propane tanks) run an EV and have A/C if we wanted. In the Winter electricity generation is much lower and water heating ands UFH will be provided by a log burner. The diesel generator may have to operate 150 to 250 hours a year, primarily in the winter. We will do all the plumbing for a  propane boiler as a back up but only buy and install it, if in the first winter it is neccessary.

Central to the Heating and DHW is a Thermal Store of at least 300 litres which enables up to 4 means of heating the store and up to 3 means of using the heat therein - all houses should have one.

We are fortunate in having large agricultural barns for installing PV and the cost of PV panels ha some down a lot.

 

Sounds interesting and you've clearly thought it through.

 

One question re: the proposed 300 litre thermal store. That capacity would be on the small side for an unvented cylinder (depending on the house size) just doing DHW, and seems potentially very much on the small size for a thermal store where you need to use heat exchangers to extract heat and want to maximise the ability to store heat from, eg, a log burner that might be run intermittently. It's doubly problematic if you're using the same store for central heating.

 

I'm no expert, but I'd guess 500 L would be the minumum you should be thinking about for this sort of thermal store, and maybe more.

[SteamyTea]

A 300 lt TS does seem quite small.

Assuming you can get away with a minimum temperature of 35°C and a max of 85°C, then:

 

4.18 [SHC of water] x 300 [mass of water] x 50 [delta temperature] x 0.0002778 [kWh factor] = 17.4 kWh.

Now my small house in Cornwall, uses, at this time of year, about 20 kWh/day, 4 of that is for DHW and everything else.

So just about enough to heat a 50 m² place when the outside temperature is around 7°C.

[Rafiki]

4 hours ago, SteamyTea said:

A 300 lt TS does seem quite small.

Assuming you can get away with a minimum temperature of 35°C and a max of 85°C, then:

 

4.18 [SHC of water] x 300 [mass of water] x 50 [delta temperature] x 0.0002778 [kWh factor] = 17.4 kWh.

Now my small house in Cornwall, uses, at this time of year, about 20 kWh/day, 4 of that is for DHW and everything else.

So just about enough to heat a 50 m² place when the outside temperature is around 7°C.

Everything I have read tells me that  it takes 1.16 watts  to heat  1 litre of water  by one degree celsius . Therefore  300*1.16*50 = 17.4Kwh. But  4 people in the household will only use circa 140 litres. So the 17.4Kwh can be roughly halved. The  Thermal Store is well insulated and loses only 1-3 degrees per day.

The other factor is the heat of the cold water entering the house. Cold water in the mains varies between 12 and 20 degrees with the higher figures obviously being in the summer. The DHW will be heated by the immersion heater from April to September only.

 

I am about to re-do my overall model and will increase the temperature from 50 degrees to 60 degrees in the summer. I also now have all the SAP calculations to double check my model. In particular I need to look at the winter month figures for space heating and DHW  in total from the SAP's  to compare with likely output from the log burner. 

 

The level of insulation etc for the house will be very high

 

Yes a larger thermal store would have been better but no room inside, we were very restricted by planning permission constraints for this rural property.

[Rafiki]

5 hours ago, jack said:

 

Sounds interesting and you've clearly thought it through.

 

One question re: the proposed 300 litre thermal store. That capacity would be on the small side for an unvented cylinder (depending on the house size) just doing DHW, and seems potentially very much on the small size for a thermal store where you need to use heat exchangers to extract heat and want to maximise the ability to store heat from, eg, a log burner that might be run intermittently. It's doubly problematic if you're using the same store for central heating.

 

I'm no expert, but I'd guess 500 L would be the minumum you should be thinking about for this sort of thermal store, and maybe more.

Yes bigger would have been better. It's actually my daughter's house and  neither I nor the rest of the family got involved in planning the project early enough, partly because most were sceptical about ever getting PP for this house on a greenfield site with no services. 

[ProDave]

Don't forget the genny needs to be water cooled with it's "waste" cooling water heating DHW or the building, aka CHP.

[SteamyTea]

1 hour ago, Rafiki said:

  it takes 1.16 watts 

kWh not watts.

 

1 hour ago, Rafiki said:

Thermal Store is well insulated and loses only 1-3 degrees per day

Have to convert that in energy loss. About 1 kWh.

1 hour ago, Rafiki said:

larger thermal store would have been better but no room inside

Can you fit it into the loft space, or outside in an insulated shed?

[Iceverge]

12 hours ago, Rafiki said:

The cost of getting connected to the National Grid

 

Have you scoped this out much? It may be possible to do some of the work yourself and save a few £. 

 

During our build I destroyed 2 X cheapo generators with a 9" grinder. Frustrated I bought a long length of 4mm² cable and dragged it 120m from the farmyard to our house. That was in addition to another 100m of wiring from the farmyard to the meter. 

 

The voltage drop was enough to upset some battery chargers but it worked. Surely 500m isn't insurmountable. 

[Rafiki]

On 09/03/2023 at 18:26, SteamyTea said:

kWh not watts.

 

Have to convert that in energy loss. About 1 kWh.

Can you fit it into the loft space, or outside in an insulated shed?

I'm afraid not.  In order to get PP the house had to be  chalet style, officially a 1.3  storey house, so very little  "loft" space. Planners wont allow a plethora of outbuildings either, other than an obligatory Bike store !

It 1.16 watts that raises 1 litre of water by 1 degree C. I know that intuitively it sounds wrong, but if you think of a kettle boiling 1 litre of water from 20 degrees that's 80 degrees increase or 93 watts on my calculation.  So you could have a 93 watt element  and wait an hour or an element 25 times more powerful ie 2.3Kw and wait 60/25 = approx two and a half minutes. My calculation may be slightly off, but it's definitely not 1.16 Kwh

In any case my simplified formula comes out to the same KwH answer as you wrt raising 300 litres by 50 degrees

[SteamyTea]

14 hours ago, Rafiki said:

It 1.16 watts that raises 1 litre of water by 1 degree C.

It is 4.18 J to raise 1g of water, 1 K.

A watt is a joule per second.

The joule is the SI unit for energy. This gets 'corrupted' to the kWh, which is 3,600,000 J.

Both the joule and the watt are derived units from the SI standards of mass, distance and time. 

 

Different materials have different heat capacities and specific heat capacities, the J/kg.K. It is more usual to use specific heat capacities when dealing with fluids, though there are times when just the heat capacity is more useful i.e. evaporation losses.

Evaporation, condensation and fusion HCs are often different for the same material.  It is what allows a heat pump to work.

[HughF]

500m away? Get it hooked up….

 

I’ve lived off grid on the isle of purbeck for 39yrs and believe me when I say, of all the services you should try and get hooked up, it’s the electric.