Air con question: does R290 expand?

[mattnotfat]

I have an air conditioning question, and it seems like most of the air con questions are in this forum?

I was thinking of fitting an Electriq Easy Fit split air con system, to cool the upstairs of the house. It uses R290 (propane) refrigerant and so can be DIY fitted.

The main thing that has put me off is the possible running cost when it's sitting unused in winter. The house is heated with a Daikin Altherma 3 split (air to water) heat pump, using R32, and if I switch the heating off when the outside temp is close to freezing the Daikin still uses a load of electricity - I believe it does this to stop the R32 freezing, expanding and cracking the heat pump.

Does anyone know if it would be any different for an R290 based system? Of course, I could keep the Electriq running in heat mode during the winter, and turn down the Daikin. But I want the air con head unit upstairs, which is already warm enough in the winter, so I would just end up with upstairs too warm and downstairs too cold.

Thanks

 

[JonathanM]

My first thought is that the freezing and expansion theory doesn't sound right. Googling shows that the freezing point of the refrigerant is about minus 150 degrees centigrade. And anyway, most liquids contract when they freeze. Also, in heating mode, the coldest bit of the system is the coil in the outside unit. Heat pumps actually defrost by briefly reversing the cycle and going into cooling mode. It's when they are working as an air conditioner that the outside coil gets hot.

I know this doesn't answer your conundum, but it might help you think of different questions to ask. I would contact the manufacturer or an HVAC contractor to get the official answer. Is this the right model? It seems to refer to an automatic defrosting mode. But I have no idea what it does in practice. Also, there may be other forums who do more HVAC stuff.

 

[ChrisJP]

Yes, water is pretty much the only liquid that expands as it freezes. So what ever is the reason that your heat pump uses electricity when it's turned off, it is not to stop the R32 freezing and expanding.
Similarly there is no danger of freezing, expansion and damage if your proposed R290 cooling system is exposed to Winter temperatures.

 

[JonathanM]

Of course, I could keep the Electriq running in heat mode during the winter, and turn down the Daikin. But I want the air con head unit upstairs, which is already warm enough in the winter, so I would just end up with upstairs too warm and downstairs too cold.

I believe you have got your thinking a bit back to front, here. AFAIK, it is when you are running the unit in heating mode that the outside unit can freeze up in cold weather.

 

[Rodders53]

AIUI, your Daikin may use a heater to keep the lubricating oil in the crank warm in the colder weather not for the refrigerant gas to protect the bearings from wear caused by oil dilution by the refrigerant. Google the issue of phantom load and ASHPs. https://heatpumps.co.uk/2013/08/13/stand-by-power-and-air-source-heat-pumps/ may help explain?

Some designs of heater and controls were poorer than other designs. More recent ones are less vampire and more mosquito I have read. There's also a mention of scroll compressors not requiring the heaters (but most domestic are likely to be swing compressors).

I've never worried about my Fujitsu or MHE aircon units' standby loads. They seem negligible when compared to the fridges and freezers.

Now asking the supplier or maker the questions should elicit an answer specific to the units you are considering. (e.g. what is "thermostat-off mode" that uses so much energy cf standby?)

This MSE thread https://forums.moneysavingexpert.com/discussion/6470914/air-source-heat-pump is interesting in that it mentions your model of A-W ASHP as having a standby load of only 15W cf a much older un-named unit taking over 100W (3kWh per day). So do check if there is some other 'vampire load' - such as the legionella cycle occurring too frequently or the 1:1 backup heater being used?

 

[ChrisJP]

...or the 1:1 backup heater being used?

Ahh yes, the little known about backup electric heater, which nearly all heat pumps have. This cuts in when the heat pump can't keep the house up to its set temperature which, in less than optimally insulated houses, occurs quite often when the outside air temperature gets down to 1 or 2C.
It's just an electrical resistance heater, so like an old fashioned electric fire and, as stated, only gives a 1:1 relationship between kW consumed and kW heat produced.
I suspect that, in Britain, heat pump owners who boast about how "toasty" their heat pumps keep their houses are unknowingly doing so quite a bit with old fashioned electrical resistance heating - and paying for the priviledge!

 

[JonathanM]

(e.g. what is "thermostat-off mode" that uses so much energy cf standby?)

The glossary on another manufacturer (Mitsubishi) website says this:

thermostat-off mode​

means a mode corresponding to the hours with no cooling or heating load whereby the cooling or heating function of the unit is switched on but the unit is not operational as there is no cooling or heating load. This condition is therefore related to outdoor temperatures and not to indoor loads. Cycling on/off in active mode is not considered as thermostat off

standby mode​

means a condition where the equipment (air conditioner or comfort fan) is connected to the mains power source, depends on energy input from the mains power source to work as intended and provides only the following functions, which may persist for an indefinite time: reactivation function, or reactivation function and only an indication of enabled reactivation function, and/or information or status display

reactivation function​

means a function facilitating the activation of other modes, including active mode, by remote switch including remote control, internal sensor, timer to a condition providing additional functions, including the main function

off mode​

is a condition in which the air conditioner or comfort fan is connected to the mains power source and is not providing any function. Also considered as off mode are conditions providing only an indication of off mode condition, as well as conditions providing only functionalities intended to ensure electromagnetic compatibility pursuant to Directive 2004/108/EC of the European Parliament and of the Council [3]

 

[JonathanM]

Could the above mean that thermostat-off mode includes the use of the crank case heater and standby doesn't?

Also, why would the thermostat-off mode for cooling be 8x more than for heating?

 

[ScottishGasMan]

Buying cheap units off of aircon direct and DIYing, while not illegal, is not a smart move.

Essentially if you have to ask those particular questions about the refrigerant then it screams out that you can not safely DIY this.

Do you have the equipment to install one? Nitrogen bottles and regulator, A3 rated Vac pump, torque spanners etc?

To answer the question no, gas does not expand in the cold, cannot freeze under weather conditions found on Earth, and is not the reason the Daikin is using so much electricity. TBH it sounds like somethings wrong with it, but I'm not overly familiar with that model, so could be fault or could just be poor design.

My advice is either get some actual training so you don't hurt yourself or others, or get someone to spec a reputable unit and fit it for you.

 

[mattnotfat]

Ahh yes, the little known about backup electric heater, which nearly all heat pumps have. This cuts in when the heat pump can't keep the house up to its set temperature which, in less than optimally insulated houses, occurs quite often when the outside air temperature gets down to 1 or 2C.
It's just an electrical resistance heater, so like an old fashioned electric fire and, as stated, only gives a 1:1 relationship between kW consumed and kW heat produced.
I suspect that, in Britain, heat pump owners who boast about how "toasty" their heat pumps keep their houses are unknowingly doing so quite a bit with old fashioned electrical resistance heating - and paying for the priviledge!

Well, the back-up heater was something I knew about when I opted for a heat pump. Overall the heat pump cost to run for the 3 years has been similar to a modern gas boiler, with a SCOP of 3.5. In the coldest weather I get a COP of around 2.2, some of which might be from the back-up heater. But with the heat pump switched off in sub-zero temperatures, it seems to use a back-up heater for something (possibly heating the crankcase as suggested above) and I've found consumption is basically the same if leave the heating on but with the flow temperature turned right down - which does at least put some heat into the building. Again, this is only in the very coldest weather, but the consumption is significant. I may be away for a month this coming winter, so instead of turning the heating off, I'll probably leave it on, with the thermostat turned down low and a low flow temp.

 

[mattnotfat]

Thanks for all your input folks. I googled whether to cut power to an AC in the winter and this https://structuretech.com/ac-breaker-off/ basically answers the question. The consumption will be the crankcase heater and not all ACs have them. If it does, it may or may not be a good idea to cut the power - some AC technicians say you should to save power, others say don't, because it's a common cause of damage.

It looks like the answer is then to get an AC unit that doesn't have a crankcase heater, and cut the power in the winter so it can't run accidentally.