Cornwall farmhouse rebuild using ICF

[dpjjones]

Hello,

 

We moved to Cornwall a year ago and are rebuilding a family farmhouse to make it well insulated, airtight and net zero energy. This is quite different to my previous day job so looking forward to getting advice and help on a range of topics here.

 

Thanks

[Marvin]

Hi @dpjjones

 

Aim to go APE 

 

It worth considering all the AIM and APE elements before making decisions. That is Airtightness, Insulation, Mechanical Ventilation with Heat Recovery OR Heat pump Ventilation, and Air Source Heat Pump, Photovoltaics and Electric Vehicle.

 

Some of these will not work properly without the others, and some will complement others:

 

1. A MVHR will not work properly without Airtightness.
2. An Air Source Heat Pump will have to compensate for the lack of Airtightness and/or Insulation to the degree that the benefits become questionable, especially during winter, without them.
3. An ASHP uses electricity and Photovoltaics can supply a little during winter and a lot during summer when cooling can be a problem and an ASHP can supply cooling.
4. PV can supply a little to an Electric Vehicle during winter and plenty during summer if your vehicle is at home during sunny days.
5. Extending a property and only doing AIM works to the extension will be no good, you have to do all the property within the thermal envelope. 

 

And thinking of running costs:

a)     Airtightness and Insulation should have no running costs and last (Well, loft insulation lasts over 40 years, in our experience) with the exception of UPVC  units for windows and doors, but that being said it will last 30 years?

 

b)    Our MVHR unit servicing 100m2 floor sized home uses about 260kWh a year; far far less than would be used to heat incoming cold fresh air in winter, and we clean the filters twice a year.

 

c)     ASHPs are, in my opinion, still in their infancy but we are now in the second year of use here. We were very careful to follow best practice in the design and installation of our system, did a lot of bespoke tweaking, and we now have an upgraded 1970’s timber framed bungalow that uses less than 20kWh per year per m2 of floor for heating.

 

d)    PV would be a lot less attractive if there is no ASHP or EV (or battery backup) or diverter to the hot water immersion. In my humble opinion, if you have a suitable roof you should install as much a physically possible. Electricity production costs (cost per kWh) are difficult to evaluate because it depends how much is used and how much is supplied to the grid. We decided to go with the PV cost divided by 7 years, which for us works out at £1.60ish per day. Yesterday the PV produced 12kWh all of which we used. Remember, 5kW of PV panels will not produce 5kW because you would have to have:

                        i.         No shadowing of any of the panels during sunlight hours (like trees, buildings or chimneys.

                       ii.         All the solar panels face exactly the right angle in relation to the summer solstice midday sun for their                                           position on the planet. (Perfect angle facing south and perfect slope)

                      iii.         solar panels completely clean

                      iv.         the sun is completely unobscured

                       v.         the Inverter is 100% efficient

                      vi.         all the other losses due to cables, and equipment, and so on.

 

e)    Knowing the above PV limitations professional installers often add extra panels to make up for these losses. (Our inverter allows us to add roughly 28% more panels than its kW rating)

f)      PV panel installations will produce about one fifth of the power in December compared with what is produced at the peak of summer.

 

g)    The electric vehicle and charging from the PV only really work well together if you can have the vehicle plugged in during the day and supply over 3kW from your PV (or a large proportion of that). This is why we went for the biggest PV that would fit on the roof.  We then installed a system which 95% of the time only charges the EV when the PV is on and generating over 2kW in winter and 3kW in summer (we have a 13amp charging system).

 

So, if finances cause you to have to consider only a few in my humble opinion AIM first and go APE later. (But prepare the property for the APE works as much as you can).

 

Best of Luck

 

Marvin