Hi All,

Just had our GSHP commissioned and all working well so far. I want to carefully monitor exactly how much electricity the heat pump uses and would like to install a meter on the heat pump supply line so it just records what the heat pump uses. I know you can buy normal electricity meters on the internet but wondering whether anyone has any recommendations for smaller units or those with extra functions like running time as well as KWH etc.

Any recommendations much appreciated.

I bought a calibrated zeroed Ampy meter off e-bay for £10 and wired it into the mains supply to my heat pump; works a treat.

Any data you would like to share with the rest of us Ted and Dantenz.

4 bed detached, all double glazed, good loft insulation, 25% of external external walls are single brick, rest is thermalite block + cavity with 25mm polystyrene. My 9.5kW air/water heat pump consumed 4875 kW/hr for heating only last year/winter. Maximum heat pump electricity consumption over a 24 hr period was 55kW/hr, overnight temp -8'C with daytime temp. of -1'C. Room temp kept @ 19.5'C 24/7 for the whole winter.

Here's the way I do it: I read my meter about once a week and also record the heating degree days (and cooling degree days in the summer). All this goes into a spreadsheet where I also note if the heating/cooling is on or off. For the periods where the heating/cooling is off, this gives me a very good idea of the "baseload" of electrical consumption for my house - for the past 2 years this is about 9.8kWh per day. In my spreadsheet, I subtract this figure from the measured consumption and also factor in the HDD/CDD data to give me a measure of how much energy is used per HDD/CDD. I've been doing this now since the GSHP was commissioned in October 2005 and it gives me a great apples-to-apples comparison of my consumption over the years which I can then correlate with the hot2000 model I have. This also gives me the ability to quantify the effects of additional insulation measures (albeit minor) over the past couple of years as the ongoing renovations continue. For example, the 1" of blown cellulose I put between the plaster and lath and the triple solid brick walls last year on two downstairs rooms saved about 10% per HDD, paying for itself in less than one season.

I find this method works well and it has enabled me to see how accurate the hot2000 model is - seems pretty good so far (within 10% of actual measurements).

I also record my gas consumption (cooking and hot water) and it's fun to watch the consumption go down when the GSHP is in heating or cooling mode :)

I think my peak consumption was around 120kWh in one day with 21C inside, -30C outside at night and -25C "high" for the day.

Paul in Montreal.

@SteamyTea, I use current HDD/CDD data as I want to correlate actual consumption with actual weather conditions. The peak of 120kWh in one day was heat (i.e power input to the GSHP and aux heaters - total heat used that day was over 300kWh), there was another 10kWh on top of that for the baseload.

For cooling, it uses about 2/3 the energy per CDD compared to HDD (something like that). The reason in cooling mode the evaporator temperature is much higher (around 24C) than in heating mode (around 6C) so there's a much greater mass-flow of refrigerant which increases system efficiency plus the evaporator in cooling mode is larger than in heating mode. The condensor in cooling mode is very cold, around 6C again so it's very effective. So even though it's been one of the hottest summers on record (around 400CDD) the cost to cool is very low - of the order of $50 or so and this is offset by the GSHP pre-heating the hot water so gas consumption goes down as well in cooling mode as well as heating.

Paul in Montreal.

@SteamyTea,

a regular A/C system becomes increasingly inefficient as the outside temperature rises as the condensor has to condense the refrigerant with lower and lower delta-T. For a water-cooled system (i.e. GSHP) this problem doesn't arrive and the condensor temperature is very low, making the system highly efficient. In some places there are GHSP systems available which just circulate the ground loop fluid to provide cooling as the ground temperature is low enough for this to work (the evaporator has to be below the dew-point of the air to be cooled to provide humidity removal). Problem with this set up is that just circulating a cold fluid doesn't provide as much cooling capacity as a phase-change approach as in a refrigerant - in other words, you can get away with a smaller coil if there's a phase change as compared to without.

One of the nice things of living in an extreme climate is that a fully-reversible heatpump like a GSHP provides the best of both worlds in both sets of climatic conditions - efficient cooling in the summer and predictable heating capacity in the winter (compared to an ASHP).

Paul in Montreal

CWatters: as I have mentioned elsewhere, the purely clip-on meters can be fairly hopeless for non-resistive loads.

Rgds

Damon

Hi there,

How did the digital ampy work out then? I am going to be installing my heat pump, and I too would like to see how it performs.

I have a 3 phase connection. Not sure if this will make it easier or harder!
Cheers
Tin

Hi adh,

The amp is a pretty good choice I think - I bought an Ampy Single Phase meter from www.universalmeterservices.co.uk for £10 (no vested interest) :-) The nice thing about the Ampy is the pulse LED which allows you to hook up a data logger like: http://www.airsensor.co.uk/component/zoo/item/energy-monitor.html to record electricity consumption in real detail which reveals quite a lot.

The data logger is easy enough - once you have the logger kit and the UartSB you download the free Arduino IDE from here: http://www.arduino.cc - plug your Data Logger into the USB port of your computer, select the com port being used and the ATMega 168 board under TOOLS and then upload the sketch (computer code) from the AirSensor website. The logger will be ready to log your meter pulses now. Complete the circuit as described which is easy enough and 'install' the sensor. Every pulse is 1 Watt and you can see when a pulse is received as the data logger has an LED which blinks - these 1W pulses are counted and every five minutes (this can be changed) the total number of watts (pulses) for that period is recorded to an SD card along with the time and date. When you want to review the data you simply remove the SD card and open the CSV files in something like Excel to graph and analyse the results. Hope it helps.

Thanks for the information. Very useful. I've ordered one for the electricity meter and one to monitor the temperatures from the heat pump to the hot water tank. The guys at airsensor.co.uk are very helpful.

These are the sensors
http://www.omniinstruments.co.uk/products/product/moredetails/adm.id1158.html

And this is the logger with SMS/GPRS

http://www.omniinstruments.co.uk/products/product/moredetails/r-log.id410.html

I am sure there are lots more and probably cheaper.

The Arduino could do it and more... however the problem is that you need to be good with basic soldering and electronics! I've just bought two Arduino Stalker boards, one to monitor the electricity useage and one to log hot water temperatures from the heat pump. It's a work in progress as I want to mount the PCB in an enclosure and allow easy access to the SD card. It's a bit of work but hopefully worth it. You can add lots of shields which will provide remote data access but again this requires some programming knowledge.

If you've got time to tinker then great, if you want an easy solution then Arduino is not for you!!

Robur,

Hoping you might be able to help. I've put together the Arduino board for logging the Ampy electricity meter. The problem I'm having is with the pulse LED on the board. I can't get it to pulse with the meter pulse. The sensor seems to be recording the pulse but the LED on the board will not pulse. It is ON but doesn't pulse which is frustrating as it makes it difficult to position the sensor without checking the SD card for correct alignment.

Have you any suggestions? I've contacted Airsensor and they have been very helpful but can't work out why it's not working either. The wiring diagram suggests putting the sensor on the 3v PIN but it was suggested I move it to the 5v PIN. However this did not resolve the problem.

Any help you can provide would be much appreciated.