Heat Pump cost data, 2nd full year

Published August 31, 2014 by Sean

My┬áHitachi Yutaki heat pump┬áhas been running for almost 3 years. I’ve made significant changes to the control logic with two external microprocessors, and have been logging data (manually and in real time). Whilst the system was a massive improvement compared with the old storage heaters/immersion heater (in terms of flexibility and control matching to heat load) the performance has been fairly disappointing from a technical point of view.

The Hitachi control logic seems optimised for steady-state operation into a load with a high thermal mass. Driving a small radiator based system it is always operating start-stop (even when there is a moderate heat load, the control logic tends to over-shoot in it’s heat output for the first 5-10 minutes of a cycle, by which time the loop is up to the trip point).

The controller will run the pump at 100% duty cycle unless the indoor temperature is clearly above the set-point. When the loop is cooling, this means heat is being pumped out to waste.

Switching between space heating and DHW is designed to run the space heating loop at a 60 degree setpoint for up to 20 minutes after the DHW target has been met. This means heating the whole space-heat circuit significantly, massive waste and inefficiency. For the communication between the two parts of the controller to function, DHW must be heated at 60 degree loop temperature)

The system was installed in November 2011. Degree days are referenced to 16 degrees outdoors (roughly the point at which domestic waste heat and insolation are insufficient to keep indoor temperature at above 20 degrees). In referring back to my post from 18 months ago, I see imeasure have (as part of website restructuring) changed the data reported for previous years (and now I see 2 different values for 2012 electricity on the site). Annual degree days is lost too. A once useful site decayed by a cute makeover… Wish I’d realised that before typing in 12 months of data this morning.

Total kWh
2010 7861
2011 9389
2012 6183 First full year
2013 5605 Better control functions

As a result of imeasure.org.uk changes, today post is void of useful data. Never rely on 3rd party providers…

I can in theory derive my own degree-day data, since I have 10 minute temperature data.

Filed under Heating

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