Heat Pump & Night Rate Meter - a no brainer?

ecowise

A few observations:
We have been running our GSHP with UFH upstairs and downstairs since Dec 2001 and have found zones effective and economical. Our heating cost so far this season for a 250 m2 house is €130 operating at night rate only (we supplement with our wood stove as needed using our own logs). If I was building again now I would build to a higher spec and rely on a MHRV (or possibly passive HRV) supplemented again with a log stove.

As to the discussion regarding the use of ASHPs at night it should be noted that (in my case anyway):
night rate starts at 23:00 hrs and ends at 08:00 hrs (advance for one hour for summer time).
The sun sets much earlier i.e. night time weather wise begins around 5pm (while on the day time rate) so a good chunk of the day time rate is actually for nighttime!

Also the temperature difference between night and day during the winter is not very big on average in our climate. It is not unusual for the temperature to rise during the night during the winter such as when a mild & damp weather system moves in from the SW after dark.

I did a simple calculation based on my weather station (west Waterford) for the months Oct-Mar inclusive and compared the average temperature for the night rate period (2300-0800h) to the average for the day rate period (0800-2300h) (making no allowance for clock change which would be very small) and calculated a night rate period average temp of 6.4 degrees C and a day rate period average temperature of 8 degrees C. Therefore operating at night only would not result in a significant performance penalty.

The problem that I have encountered with thermal modelling of houses is that the only way to do it properly is with a physics based simulation engine and that takes a lot of time to set up.

Water John

Excellent post, Ecowise.