In the UK, we had a couple of cold spells this winter - one in early December and one in late January. It looks like we might have another one next week. I'll do a specific post about the energy usage during those periods in the next couple of weeks. This post though is about the Daikin service support that we got regarding some questions we had about our heat pump.
Our heat pump had been covered in frost and/or ice for most of the days of the cold spells and we hadn't seen a defrost cycle happen. The heat pump is not directly visible from the house, so it was possible that we were missing them but the build up on the coils and the fact that a defrost usually releases an obvious plume of steam meant that we were unsure if this was happening. The electrical draw had been getting bigger and bigger as the cold weather continued - often reaching more than 9 kW! The greater the electrical draw, the greater the daily cost (especially with energy prices where they are this winter). The temperature outside during these periods was roughly -1C and our main query was "should the power draw be that large - we thought it was going to be about 4-5 kW max?".
Our heat pump had been covered in frost and/or ice for most of the days of the cold spells and we hadn't seen a defrost cycle happen. The heat pump is not directly visible from the house, so it was possible that we were missing them but the build up on the coils and the fact that a defrost usually releases an obvious plume of steam meant that we were unsure if this was happening. The electrical draw had been getting bigger and bigger as the cold weather continued - often reaching more than 9 kW! The greater the electrical draw, the greater the daily cost (especially with energy prices where they are this winter). The temperature outside during these periods was roughly -1C and our main query was "should the power draw be that large - we thought it was going to be about 4-5 kW max?".
We ultimately found that during cold weather (anything below 2C it seems) the coils started to frost/ice over as expected but that saw no evidence of a defrost session happening. The advice from the installers was that the heat pump should automatically be defrosting itself 2-3 times a day but that the coil was looking very frosted. The heat pump was also running very, very hard, with the sound recorded at almost 60 dB (it was supposed to be about 42 dB) and the power consumption frequently being high (8-9 kW during these iced/frosted periods). From talking to other owners this didn't seem like it was running as it should, although it runs great when the weather is warmer.
We organised for a Daikin engineer to come and have a look. He was absolutely brilliant - attentive, informative, patient, thorough and as engaged in getting an improved efficiency as we were. The following bullet points summarise his visit:
- He noted that the heat pump is a 14 kW unit and noted that ~6 kW was required by the house based on the heat loss calculations done for the initial install.
- He watched the videos we had taken of the frosted coils and looked at the energy usage plots that I had taken screenshots of and wasn't concerned. He was confident that the defrost mode is working as designed. He did think that the energy draw was high.
- He ran the unit for just over an hour and noted that the compressor was working hard on start up but that the once it ramped down there was no cycling at all. He calculated efficiencies of 3.5 - 4.5. Outside temperature at the time was 5C.
- Given the size of the unit compared to the heat loss, he lowered the weather comp curve from 48C @ -2C to 42C @0C
- As we discussed it and he gathered data he thought that the backup heater could have been the cause of the high kW draw during cold weather. Given the size of the unit he decided the backup heater is likely not needed and so it has been set to operate at -10C outside air temperatures (or if the water temp falls to 18C as designed)
- He updated the controller firmware for us
- Noise from the compressor and fan was measured at just under 60 dB at 1 m with the compressor exposed, which he deemed was within a suitable tolerance (this is something we aren't sure we agree with!)
- He checked the magnetic trap which stops metal particles entering the heat pump and could reduce efficiency if blocked, and that was clear
- He was impressed with the flow rate and efficiencies obtained and commented that he thought it was a really good set up, installation and commissioning
- He called us on the phone later in the day to get me to tweak a setting in the controller that he'd been mulling over as he wrote up his service report, which I thought was brilliant customer support.
This post relates to the earlier post on customer support. The best thing for us from the visit was peace of mind that the system is now running more efficiently, reducing consumption and our bills. We've also seen the heat pump in defrost mode (pretty impressive steam clouds!) and the draw is usually between 1.5 kW to 5.5 kW depending on the air temperature and whether the compressor is running.