Reply To: Very high energy bill in 8 year old house – no apparent cause

[Sarah Grant]

Hi Ian and Norman,

Thanks very much for your input. I went over the lighting in detail (chimney effect, cost to run, inefficiency of the incandescent bulbs etc) with the customer and also recommended upgrading the fittings to IC-F rated ones and installing insulation over the top, as well as replacing with LED bulbs especially in the high-use areas.

I’m also wondering what sort of effect the waste heat from the lighting would have on the HRV system? Given that there’s 21 100W incandescents running for around 8 hours a night with heat being sucked straight up into the roof space, this would surely warm the air in the reasonably well sealed roof space (like having a 2.1KW heater going in the roof space for 8 hours a night) meaning that the HRV would turn on more regularly because there’s a differential between the warm roof space and the colder house that it’s trying to circulate warm air into?

Consequently, the HRV system is likely to be working full time during the lighting period (as well as during solar heating of the roof space). If the homeowner replaces the light fittings with IC-F rated fittings and fixes the insulation gaps, the small amount of waste heat from the LED’s would remain in the room rather than heating up the roof space. Would this not then reduce the amount of time the HRV system is operating because of a lower temperature differential between the roof space and the room(s), saving them money on electricity?

Does anyone have some good technical info on ventilation systems? I’ve had a really good look around online and I can’t seem to find anything that tells me what the power consumption of the fans/heating units/ typical power consumption etc are.

Cheers,
Sarah

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