Is my heat pump costing me a fortune while it sits idle in Summer?
Graham Hendra
Heat pump product development engineer. Author of heat pump text books. Heat pump builder.
If you were to take the cover off your heat pump and use an Amp clamp you could see exactly how much energy it was using sitting there in the sunshine doing nothing.
If you did this you would get a reading not unlike this one above. 0.459 Amps. At 240 Volts according to my school boy electrics I x V = Watts means the unit is drawing 230 Volts x 0.459 Amps = 106 Watts. Yikes that's horrible. Every day it uses 2.5kWhrs of electricity and at 33p a unit that's ￡0.83 a day. What? I get nothing for ￡0.83 a day that's ￡303 a year, quick power it off its costing a fortune.
Ok stop a second, if it was using this much current and it was burning 106 Watts standing idle it would be hot, that 106 Watts has to go somewhere. Last time I looked everything in the unit was cold or at least ambient temperature.
But before everyone panics there is a small issue with all of the above, its not true, your Amp clamp is assuming the voltage across the unit is 230 Volts, but its not, its an induced Voltage, the unit is drawing 0.459 Amps but its not at 230 Volts. When you are dealing with electronics and small currents you really need a Watt meter to measure what's going on (no pun intended).
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So if I put my Watt meter in circuit you can see its actually using 14.1 Watts . A watt meter measures both the current and the Voltage it does not assume anything.
So in reality the unit uses a kWhr of electricity every 71 hours or 122 kWhrs a year. or ￡36.79 a year at 33p a kWhr.
Phew and relax.
Oh and just in case you wondered, your boiler is drawing current sitting there doing nothing too. No one talks about how much electricity a boiler uses per year. Maybe they should.
Entrepreneurship & Real Estate
1 年Wow. Glad I found this post. This same thing is happening to me with a Trane AC (it’s a heat pump model). It is a Trane 5TON Compressor for a VRF system. In my case this idle/vampire draw equates to to around 5kwh per day or 150 kWh per month. Which in my country is around 35 USD. For me this is to high a cost for something always off. I am seeing the consumption on my breaker panel as I have an emporia energy monitor system installed - so it is real. I have a 16ton compressor which uses 4x lower idle draw from the same brand. Only fix I have found is turning off the breaker. Any ideas? It’s not the CCH (I took it off)
Emerging Technologies Director at Kensa
2 年A few years ago I came across a homeowner who turned off their PV inverters overnight as they used a few watts when in standby. He used to get up at sunrise every day to turn them all back on. I will be honest, I have told friends and family to shoot me if I ever become like that!
Expert Witness Building Services Engineer at Ridge & Partners
2 年Really interesting, thanks! I came across the crank case heater explanation on an early heat pump. The electricity meter was reading a minimum of ~200-300W per heat pump (each had 2 compressors). This was really impacting the seasonal performance factor (since each compressor spent more time off than on). When challenged on why they don’t put a thermostat on crankcase heaters, none of the manufacturers said they didn’t actually use crankcase heaters. Your blog is now making me question what I thought I understood here! I wait with interest for a piece on alternatives to crank case heaters.
Metering infrastructure and meter data management services for developers, building managers, and utility companies
2 年Disagree Graham Hendra 1) 14 watts on "standby doing nothing" is fucking appalling in this day and age. Which manufacturer is this who still thinks that's acceptable? 2) Some are far worse than this. Mitsubishi Ecodans come to mind - though only certain models. Their techies answered the query about why the standby is high once upon a time (horrifically inefficient crankcase heating strategy) but the commercial folks now deny the response ever came from Mitsubishi and refuse to be drawn on standby consumption. It's a great question to ask the distributor though. "Can you warrant, in writing, that the standby consumption of this device is <1W?" I wonder if anybody would...
Senior Mechanical Engineer at ESB Smart Energy Services
2 年Great article, loved the ending ??