Air Source Heat Pump - general question

[joe90]

27 minutes ago, SteamyTea said:

Yes, if I can disaggregate the data.

Great, not top of my priority list at the mo but perhaps at a later date 👍

[Marvin]

2 hours ago, ProDave said:

This is proving to be a question that should be asked of the manufacturer BEFORE you buy an ASHP as some are proving to have high standby power use.

 

My own, a 5kW LG Therma V use used 1kWh in the last 6 months of standby.  That's 1kWh in about 4000 hours which is an unbelievably low standby power level.  Yours would have used 320kWh in the same time.

Your right, I have seen no info about standby power usage. However having checked the calibration of the plug-in monitor I find that its suggesting that our mains is 200V when actually 243V so results would be different than the 80-90Wh measured, but certainly not down to your level.

 

[Marvin]

2 hours ago, ProDave said:

Be careful.  There is a long thread about this with Ecodan units.  Some use a sump heater, and the manufacturer said something like the sump heater should be turned on for a few hours before starting the unit.  So your simple timer might end up doing harm if the cause of the high consumption is a sump heater.

From manual. Is this what you mean:

 

First boot-strap or starting up again after being shut down for a long time, stop, ensure power is on ahead and heating at least 12 hours for crankcase (local loop temperature is zero). Water pump starts up first, fan starts up, and then compressor starts up and begins regular operation.

 

Actually, I wonder what the sentences do mean!

 

Edited September 15, 2022 by Marvin

[ProDave]

7 minutes ago, Marvin said:

Actually, I wonder what the sentences do mean!

I think that would translate to:

 

If you have not applied power and left it for 12 hours for the crankcase to heat up, then we won't be liable for a compressor fault if you demand it to start too soon.

[PhilT]

52 minutes ago, joe90 said:

I took the clamp off recently as had to work on the CU, but can put it back on I guess, but will it tell the difference from other stuff (STP)?

A clamp meter will give the wrong reading (see attachment from Mitsubishi). From the thread on Ecodan standby power consumption, there is some evidence, based on actual meter readings, that the resistive standby heating for single phase models draws around 40W on average, with a step change over/under 21degC.

Standby Power Consumption (1).pdf

[Marvin]

52 minutes ago, ProDave said:

I think that would translate to:

 

If you have not applied power and left it for 12 hours for the crankcase to heat up, then we won't be liable for a compressor fault if you demand it to start too soon.

Making some enquiries...

[SteamyTea]

36 minutes ago, PhilT said:

see attachment from Mitsubishi

So they admit it is a problem but have put some PR spin on it.

For the two models that have a 94 W mean load when greater than 21°C (is that outside temperature) a resistance heater would do all my hot water.

[PhilT]

1 hour ago, SteamyTea said:

So they admit it is a problem but have put some PR spin on it.

For the two models that have a 94 W mean load when greater than 21°C (is that outside temperature) a resistance heater would do all my hot 

I can't speak for the 3 phase models but the latest single phase 11.2kW model is keeping us cosy using only 3k kWh pa against an EPC heat loss calculation of 16k kWh pa. The standby draw is a small price to pay to achieve that level of efficiency. If you have another way of heating DHW you can switch it off in the summer 

Edited September 15, 2022 by PhilT

[SteamyTea]

10 minutes ago, PhilT said:

11.2kW model is keeping us cosy using only 3k kWh pa against an EPC heat loss calculation of 16k kWh pa.

That implies a CoP of 5.3, did you do other work to the house as well, or have different family circumstances?

Or your old heating method was horribly inefficient.

Edited September 15, 2022 by SteamyTea

[PhilT]

1 hour ago, SteamyTea said:

That implies a CoP of 5.3, did you do other work to the house as well, or have different family circumstances?

Or your old heating method was horribly inefficient.

No to the first part but yes, my old heating method was horribly inefficient. My gas usage was 21,000kWh pa implying boiler efficiency of 76%. But even if EPC was overstated by 20%  SCOP would still be well over 4.

[JohnMo]

I suspect there are lots of really inefficient gas boilers out there.  Not the boilers fault, oversized by the installer, running to hot, multiple zones, short cycling like no tomorrow.

 

Just like lots of new heat pumps are going to be, but gas boiler poor quality install is hidden by the historical low price of gas and a customer base that doesn't know anything else.

[dpmiller]

I do wonder how accurate the readings of power analysers are vs certified meters, especially at the low end and with odd power factors...

[SteamyTea]

4 hours ago, dpmiller said:

I do wonder how accurate the readings of power analysers are vs certified meters, especially at the low end and with odd power factors...

Why I created a logger than reads the pulses off the certified one.

[Marvin]

Hi @ProDave

 

To all ASHP owners! 

 

I do not know if your ASHP is the same as mine but it seems that all ASHP compressors have a 'use warm oil' requirement.....

 

Know this:

 

The manufacturer of my ASHP kindly responded to my enquiry regarding starting the ASHP back up after the ASHP being off for a long time.

 

The ASHP compressor has oil in it, which needs to be warm to avoid excessive wear due to the oil's viscosity.

 

It is recommended to put the ASHP on standby for at least 12 hours before firing up if the outside temperature is 6°C or below to give time for the oil to warm. 

 

Completely turning off and on the ASHP came up as a discussion because of the amount of power used in standby mode. 

 

Good luck.

 

Marvin

 

 

[joe90]

@Marvin that’s very interesting and makes sense, as I plan to time mine I need to find out my parasitic load and manufacturers instructions, well done 👍

[Garald]

1. Insulation is a priority, particularly if you have a rating of G: the best thing you can do in terms of energy is needing less of it.

2. If you don't want to or can't change any of the radiators, or if you can do only a middling insulation job, you may want to consider a high-temperature ASHP. (I was considering high-temperature ASHPs for my renovation job, until I took the plunge and decided go low-temperature.) It's certainly less efficient, and also, typically, somewhat more expensive (enough that it may eliminate most of the savings coming from not needing new radiators). They are designed for (less-than-total) renovation jobs.

3. On air-air: they are actually common in houses in the US South. There have to be some ways to diminish the noise. (I would be bothered by it.) Worth considering perhaps?

[ProDave]

45 minutes ago, Marvin said:

Hi @ProDave

 

To all ASHP owners! 

 

I do not know if your ASHP is the same as mine but it seems that all ASHP compressors have a 'use warm oil' requirement.....

 

Know this:

 

The manufacturer of my ASHP kindly responded to my enquiry regarding starting the ASHP back up after the ASHP being off for a long time.

 

The ASHP compressor has oil in it, which needs to be warm to avoid excessive wear due to the oil's viscosity.

 

It is recommended to put the ASHP on standby for at least 12 hours before firing up if the outside temperature is 6°C or below to give time for the oil to warm. 

 

Completely turning off and on the ASHP came up as a discussion because of the amount of power used in standby mode. 

 

Good luck.

 

Marvin

 

 

There was a lot if info on the Ecodan standby power thread.  Not all compressor types need a sump heater, scroll compressors were one type mentioned as not needing such a heater.

 

My LG Therma V ASHP, I have installed  an electricity meter (old dual dial E7 meter) that separately meters power used while heating DHW and while doing space heating.  In the summer it perhaps does an hour a day heating DWH the rest of the time it is on standby doing nothing.  That standby time is metered by the "space heating" dial on the electricity meter.  It has only clocked up 1kWh on that dial in the whole of the summer.

[PhilT]

33 minutes ago, ProDave said:

There was a lot if info on the Ecodan standby power thread.  Not all compressor types need a sump heater, scroll compressors were one type mentioned as not needing such a heater.

The tech blurb for Copeland scroll compressors says that some do and some don't; HPs with a coolant charge above a certain level need compressor heating to prevent the coolant compromising lubrication and start up. Sounds like LG and Mitsubishi have adopted different approaches; lower coolant charge/no compressor heating vs higher coolant charge + heating which would only make sense if higher coolant charge gives better efficiency

[ProDave]

8 hours ago, PhilT said:

The tech blurb for Copeland scroll compressors says that some do and some don't; HPs with a coolant charge above a certain level need compressor

So is that related to HP size?  Mine is a small one, only 5kW so is that why it has low coolant charge and does not have a sump heater?

[Marvin]

33 minutes ago, ProDave said:

So is that related to HP size?  Mine is a small one, only 5kW so is that why it has low coolant charge and does not have a sump heater?

Ours is a 4.3kW. Perhaps it is related to compressor design? 

Edited September 17, 2022 by Marvin
minor change.

[JohnMo]

It's all to do with the way the compressor fluid and the compressor lube oil interact.  If the compressor fluid is in a liquid state and can mix with lube oil, the lubricity of the lubricant is comprised, hence a need to heat the oil before startup.  The heating drives the compressor fluid out of suspension.

 

However some compressor designs limit or exclude the interaction between lube oil and compressor fluid, so no pre heat is required.

 

Different design approach taken, one gives better standby performance, the better running performance.

[PhilT]

This is the text from the Copeland tech manual on their scroll compressors: http://www.hvacrinfo.com/cope_ae_bulletins/TAE1312.PDF

(for those using resistive heaters the principal still applies)

 

Crankcase Heat - Single Phase
Crankcase heaters are not required on single phase compressors when the system charge is not over the 120% limit shown in Table 5. A crankcase heater is required for systems containing more than 120% of the compressor refrigerant charge limit listed in Table 5. This includes long line length systems where the extra charge will increase the standard factory charge above the 120% limit. Experience has shown that compressors may fill with liquid refrigerant under certain circumstances and system configurations, notably after longer off cycles when the compressor has cooled. This may cause excessive start up clearing noise or the compressor may lock up and trip on protector several times before starting. The addition of a crankcase heater will reduce customer noise and dimming light complaints since the compressor will no longer have to clear out liquid during start.

 

"dimming lights complaints" lol. The above and table 5 imply that heat pump manufacturers may charge their circuit to more than 120% of the "charge limit" for reasons unknown but possibly efficiency gains? Lending weight to the hypothesis that Mitsubishi do on the models burning 40W for example, but LG don't - for example the model cited in an earlier reply which had effectively zero standby draw.

Edited September 17, 2022 by PhilT

[JohnMo]

It really talking about air conditioning heat pumps, where there is a requirement to overcharged over a fixed pipe length between indoor and outdoor units.  Same is true for a split ASHP, but not mono blocks.

[dpmiller]

"single phase" there means it doesn't apply to any inverter units as they use a 3-ph compressor and slowly ramp up speed, automatically clearing down gently with no "protector" to trip out anyway...

[ProDave]

47 minutes ago, PhilT said:

This may cause excessive start up clearing noise or the compressor may lock up and trip on protector several times before starting. The addition of a crankcase heater will reduce customer noise and dimming light complaints since the compressor will no longer have to clear out liquid during start.

That sounds like the startup of an old freezer we keep as a standby and only gets used once in a while.  At first start up the compressor appears to be locked and just sits there humming.  The power trips off using a device called a klixon (sp?) .After several tries it starts.  I assume the periods it runs for a few seconds stalled, the motor windings are heating things up until it frees up.