Midea Heat Pump expensive to run

matelodave

Have you looked at the DHW schedule or timers. Somewhere in the heatpump controller menu will be a function to schedule heating and hot water times and temperatures. 

https://www.bing.com/videos/riverview/relatedvideo?q=midea+heat+pump+timer+schedules&mid=130ECB4F6EF7880E45F8130ECB4F6EF7880E45F8&mmscn=stvo&FORM=VIRE

and here - https://www.bing.com/videos/riverview/relatedvideo?q=midea heat pump timer schedules&mmscn=stvo&mid=CA3F9F4D301E34CA4A34CA3F9F4D301E34CA4A34&ajaxhist=0

Have you got a manual, if not have a trawl of t'interweb for the Midea site and download one so you can understand what all the functions mean (get both the operating manual and the commissioning instructions for your specific unit and controller) Its better than stabbing in the dark.  

Write down the settings that you've got so you can always revert if you totally muck it up. Only change one thing at a time and give it enough time to settle down for you to check whether you need to re-tweak or un-tweak, ideally at least a day and dont forget to take the weather into account. Log what you did, when you did it and the result to get a picture of what is happening. 

We've had temperatures differences between -8 last week and +10 this week which can have quite a dramtic effect on your consumption. That's where a smart meter helps, you can log consumption in half hourly segments

I can set multiple times, temps and operations (on/off) for the heating and hot water for each day of the week which allows the hot water to come on either once, several times a day or continuously. The same with the heating which allows different temps at different times on different days. I'm guessing that you haven't yet discovered that feature but it will ensure that the hot water isn't on continuously.

We just heat hot water for an hour or so at 45 degrees in the mornings and that gives us enough hot water for a couple of showers plus any other hot water that we need.
Dishes go in the dishwasher and if we want really hot water for a greasy pan then we boil up as much as we need in a kettle.

Painter23

Thanks a lot @matelodave.
The Midea 'customer handover booklet' the installers left behind is nothing more than a diagram of the controller interface but it doesn't show show any operation of the system. They emailed me the installers manual but, again, this is so vague it's just the initial set up of the system for an engineer rather than how to understand it.

I'll have a good trawl through YouTube this week to try and get familiar with it.

Painter23

Hi guys, thought I'd give you a bit of an update on my heat pump journey a couple of weeks in.

I'm now living in the property and have been following the learnings of the last few pages.

I was finding the house quite warm even at 18 degrees (according to the Hive thermostat, which is only used as an overshoot mechanism at 23 degrees) so I've been experimenting with adapting the weather compensation curve with reasonsable results.

However, what I've realised is that the compressor is only coming on periodically even though the system is 'on' permanently. I'm imagining this is what's called cycling? It maybe does it once every couple of hours or so when the fan also comes on (and the 'petrol pump' symbol comes on the controller). My questions, therefore, are:

• Assuming the compressor/fan shouldn't be cycling on and off how would the pump ever stop just heating and heating the house til it got too warm?
• I assumed that even though the pump is 'on' 24/7 it periodically 'slows itself down' or stops sending as much hot water to regulate the heat?

One interesting bit I discovered was that the pressure gauge next to the tank was showing less than 0.5 bar and, going back over old photos, may have been like this for ages. I topped this back up to 1.4 bar and it's been hovering around that mark for a few days. Assuming it was not operating efficiently with such low pressure but there were no error codes showing.

I have taken out a service package with Midea so will be getting them to service it shortly.

benson1980

At slightly milder outdoor temperatures the ashp will oscillate around whatever the climate curve set point is so what you describe is normal. The mideas will only really run continuously when a bit colder, but not so cold that it will then need to be running defrost cycles. The continuous runs tend to be when it is between 4 to 6 ish degrees C outside.

The circulator pump will run continuously when the heating is on. That is normal.

Pressure should be where you've set it now.

Painter23

Thanks @benson1980 - so it's normal for the fan and compressor to cycle on and off because it's reaching the weather temps more easily? But as it gets colder is working harder and more continuously to keep the temp required?

What is the circulatory pump? Is that the constant 'hum' you hear from the pipes inside regardless of whether the compressor/fan are activated?

NedS

There are two ways a heat pump can reduce it's output.

The first is that the compressor can modulate (reduce) it's frequency - the lower the frequency the compressor runs, the less the power draw and the less heat output. You set a desired flow temp via your weather compensation curve and the heat pump starts heating the water circulating in the radiators (or UFH). If the return flow temp is coming back too high (because the radiators can no longer emit the heat), then the heat pump will first reduce it's output by slowing the compressor (typically down to around a quarter normal peak output).

If the heat pump is still putting out too much heat (maybe because it's very mild outside), then it will temporarily turn off the compressor (known as cycling) to give the circulating water time to cool before turning back on again. During this time the circulation pump may continue to run or may also turn off (depending on the heat pump and how it's configured). The circulation pump is the water pump that pumps the water from the heat pump around the heating circuit (radiators or UFH) and back again. You may hear the pump running or hear the water circulating. On some installations this pump is located outside in the ASHP box, and on others it will be indoors near the hot water cylinder / plant room.

Painter23

Thanks @NedS, so based on that logic would lowering the flow rate help reduce cycling as the lower temperature is less likely to cause radiators to struggle to emit the heat? Or is it relative to the weather curve anyway so negligible ?

matelodave

I know you've got a Midea heatpump but you might find this interesting regarding weather compensation curves - the principle will be similar - https://energy-stats.uk/vaillant-arotherm-weather-curve-information/

This is also quite interesting - watch it all as there's some useful info towards the end -

https://forum.buildhub.org.uk/topic/41853-can-the-flow-temperature-be-too-low/

and this - https://www.youtube.com/watch?v=0oszaqP0TI4

There are a lot of variables, not least the weather and they all interact with each other https://energy-stats.uk/heat-pump-cycling/

As said earlier, don't randomly prod and poke. Have a plan, only change one thing at a time, leave it to settle down and record the results. Are all your radiators properly sized and balanced and what are your flow and return temperatures.

Having a shiny new heatpump is a different experience to having a boiler and some understanding will help you get the best out of it. There's loads of info on t'interweb which can help you understand what is going on and to prevent panic and anxiety. I spent the best part of two winters trying to tweak mine in conjunction with all the random extra controls (a zone for each room) until I chucked them all away and just let it get on with it using weather compensation. Adjusting the flow and w/c curve down until we were comfy also reduced the amount of cycling although it does increase a bit when it's mild outside as you'd expect.

benson1980

This is what your ashp will be doing- pink line is the climate curve set point. Green the outlet temp, overshooting this set point and then cycling. My orange line down the bottom is outdoor temp.

It is difficult to optimise or really see what is going on unless you plot the data via the modbus interface inside the control panel. This is beyond the interest of most people, and perhaps beyond what is necessarily required. Depends how interested you are.

The flow rate can't be altered (as far as I am aware).

Balancing might need addressing but fundamentally if your indoor temp is to your liking and cost-wise it is in the right ball park, then again might not be strictly necessary (or might have already been done well).

As suggested via pm if you want some more detailed advice and steer to optimising the midea unit I'd recommend heading across to renewableheatinghub forums where there's a few midea owners who are very knowledgeable.

Painter23

Thanks a lot guys. Comfort levels are very high but difficult to gauge the energy consumption as I'm running a large dehumidifier and fan 20 hours a day to dry out a leak.

I'll try looking at that other forum too and see how much i elicit from Midea when they come to service it.