Altherma HT ASHP - power consumption whilst idle

Hi,

I have a Daikin Altherma HT ASHP and have been experiencing higher than expected electricty bills. So I bought an energy monitor and the reason became apparent immediatley.

When the system is doing nothing i.e. niether space or hot water heating, it is still consuming 200w per hour. This doesn't sounds much but it soon adds up over a month and is a significant increase on my bill :-(. When the system is operating (space or hw) the consumption seems normal.

The system is literally doing nothing - both the indoor and outdoor unit are silent and inactive. Is this idle consumption normal? For a tecchnology that is supposed to be energy efficient and green, it seems alot of consumption for no benefits.

The 200w consumption is roughly spit equally across the indoor and outdoor units. Any advice much appreciated.

tks

Hi there,

Whilst I'm not intimately familiar with this particular heat pump, a small amount of standby energy usage is common for almost all HVAC&R systems. In the case of a heat pump most of the energy is probably used by the compressor sump heater - used to prevent liquid migration/dilution of the oil & reduce wear on startup. I'd also expect the controller to use standby power, with time clock, schedule etc. In fact it is common for manufacturers to stipulate that compressor sump heater must be energized minimum of 24hours before compressor operation.

However it is possible that the unit might not be operating at optimum efficiency, (dirty filters, dirty coils, correct refrigerant charge etc), service should clarify that.

Often the reason for increased dollar value of electricity bills is rise in unit cost of electricity and/or changes to peak/shoulder/offpeak times (if using smart meter).

tks for the informative reply - much appreciated. Its using 5kw of standby energy per day - do you think this is excessive and an indication that the unit is not running efficiently?

Many Tks

Standard (standby) sump heater wattage is 200W to 500W instantaneous value. If the unit is not operating correctly it would likely use more power during operation and/or run for longer to achieve desired conditions. If in doubt get a reputable service agent or technician to check it out.

Is the energy meter by any chance a clamp on current reading device? if so you will not get true readings of consumption on an inverter driven unit by employing this method, need to wire inline watt hour meter for true consumption figures in standby. Disregarding sump heater this should be minimal, Mitsi units send current around compressor casing for example and the variation between energy consumption indicated on clamp meter and as measured are huge. As per the above post power and energy should not be confused as power consumption does not take into account the period of time running at a particular output and seeing as you buy electricity in kWh (energy) then this is the figure that matters and needs to be quantified.

The unit is not faulty.

I have one in our house and it uses around 220w in standby on our enrgy monitor.

I agree though it's not good especially in the summer months.