it's hard to compare different houses because they are all so vastly different, form some houses 10,000kwh/year is tiny, for others it's massive
if you have an MHRV and are surviving with a 0.7kw exhaust air heat pump then your house must be very efficient
heat pumps are best used if you can use low level heat to warm your house - underfloor heating is the best example but massively oversized radiators etc.. can work well too
with a home as efficient as yours it seams crazy to me not to use solar thermal - you'll have 'free' heating and hot water for 9 months of the year
chances are your heat pump has hardly run all summer (do you have bills to track your usage?)
and then once winter has hit they've struggled to provide the heating/hot water you need to are running flat out
it's hard to really know what's going on without more numbers to work with... but I just did some quick maths and....
if you're using 10,000kwh/year
if 700khw is for the MHRV
and 3,300 is for other use (fridge/tv etc...) (just short of 10kwh/day)
then that would leave you with 7000kwh for the heat pumps (combined).... which is enough to run both of them 24/7 for 150days
it might be best if you buy a data logger to track your power usage before you start your renovations... at least then you will know exactly what's going on..... it would be a terrible shame to have all that work done and then fine out that the main problem was elsewhere (lacking in insulation, air leaks etc...)
I don;t really know much about data loggers.... but I'm sure someone here could advise you
data really is kind here... and will help you pinpoint exactly where all your power is going!
