Lessons learned from last ready - getting ready for cold snap

[S2D2]

17 hours ago, billt said:

Mine is defrosting all the time.

 

 

It's been very humid for a few weeks, lots of rain, and cold.

 

However, the reason is almost certainly that I undersized the heat pump in an effort to run it efficiently. The system was designed for -3C with a flow temperature of 35. The result is that the heat pump is running continuously at full output, so freezes up quickly. It is maintaining an adequate indoor temperature at low outdoor temperatures, but there's no leeway.

Which model heat pump is this please? What is your overall CoP so far?

 

My A2A was defrosting once an hour at the worst conditions, heating air I guess makes it less likely to get stuck in "catch up" mode, but the gas boiler comes in more often as a result.

 

I'm on Cosy with a home battery and just gave up messing with temps during the peak periods and let it run constantly other than in the peak period. There just isn't enough storage capacity with air even though the CoP hit was acceptable.

[billt]

It's a Samsung Gen 6 8kW. It was cheap and I was trying to spend as little as possible, unfortunately spec creep occurred and tthe system ended up more expensive than initially expected. I would have done better to have spent an extra 2k on a Vaillant Aerotherm+. Isn't hindsight wonderful?

 

The SCoP is 3.97. For the first few weeks it was about 4.4 but the cold damp weather has had its effect.

 

 

[HughF]

I’ve been away from my system all week and I haven’t had my wife on the phone saying the heating has gone off, so that’s a start…. Back there today so will see how things have been. Will likely remove the nighttime off period 23:30-05:00 now it’s basically 1 degree all the time.

[JohnMo]

1 hour ago, HughF said:

it’s basically 1 degree all the time

Nice toasty -7 last night for us, with a high of -1 forecast today and -8 tonight. But plenty of clear sky so hopefully a decent amount of solar to power the heat pump 

[ProDave]

Last night was the first day the really cold weather reached us, -6 last night.  Most of the week it has barely dipped below 0.  And none of this "heavy" snow has reached us yet, at least not at our level.  The tops of the hills are nice and white though.

 

Heat pump here still just running on it's normal daytime times, off at night.

[eandg]

On 29/11/2023 at 23:41, SuperJohnG said:

I've not seen a defrost yet since installed- 7kW Vaillant unit, commissioned in May. Running on weather comp, single zone for whole house , which is 265m2, and heating only downstairs. 

We'll have the same unit and have the same set up with heating only downstairs, though the house is about a quarter smaller than yours (208m2).

 

UFH set for 21 between 7am and 10pm and yesterday was our highest use yet, using 34kWh of electricity all told (which includes for the usual dishwasher, oven, showers, washing machines on etc). I'm not sure how we find out about defrost settings, heat demand and calculate if our flows are right etc. but does that sound reasonable enough (or not excessive enough to spend my weekend working out how to make the set up more efficient)?

[HughF]

Sounds just fine, a bit less than us but we do a lot of tumble drying... I think we've done 50 on the whole house today. It has been hovering around freezing and lots of laundry has been done.

[JohnMo]

I have managed to use 47kWh all in today (6kwh from solar), but was messing with thermostats and managed to leave one in manual: so have had the heat pump running for about 6 hrs more than planned, without realising. But currently -7 outside and due to drop to -9 in the next hour or so.

 

But floor is well charged with heat.

[JoeBano]

Yesterday it was -3c all day here noticed my heat pump was short cycling a lot not really getting any heat downstairs either. My mixer on Ufh was set to 35c and flow temperatures on the heat pump were maxed out at 45c. Set to max on the mixer seem to stop the short cycling floors warmed up nicely. 

[JohnMo]

On 28/11/2023 at 06:42, Conor said:

All good? Nope, because the house had lost enough heat energy, and it was cold and damp outside, so that the heatpump really struggled to bring the temp back up to our desired comfort level. Lots of defrost cycles etc

Just found myself in the same position. Had an extended ASHP run a couple of days ago and yesterday the house thermostat switched off the heating at 8.30 am. The temperature haven't been above zero for a few days and a couple of days at -7. We had also been using the log burner.  All good thinks me. It's cold but I decided to make some mods to the heating system to allow me to flow at a higher temperature to heat the summer house also.

 

Fired up the heating just before tea time yesterday and found the flow temp way lower than set point. Think what's happened is floor has lost it's temperature and I am having to recharge it, the very low return temps are not allowing the flow temperature to increase to set point; heat pump is managing dT. Over last 18 hours we have had quite a few defrosts and the flow temp has increase 3 degrees. Still some charging up to go.

[Andehh]

19 hours ago, JohnMo said:

Just found myself in the same position. Had an extended ASHP run a couple of days ago and yesterday the house thermostat switched off the heating at 8.30 am. The temperature haven't been above zero for a few days and a couple of days at -7. We had also been using the log burner.  All good thinks me. It's cold but I decided to make some mods to the heating system to allow me to flow at a higher temperature to heat the summer house also.

 

Fired up the heating just before tea time yesterday and found the flow temp way lower than set point. Think what's happened is floor has lost it's temperature and I am having to recharge it, the very low return temps are not allowing the flow temperature to increase to set point; heat pump is managing dT. Over last 18 hours we have had quite a few defrosts and the flow temp has increase 3 degrees. Still some charging up to go.

 

Not a dissimilar position to what I found myself in last week! Let the floor get too cold experimenting in the cold weather and there wasn't the warmth to enable the defrost cycles to run effectively vs getting raw warmth into the slab! Lots of energy for little true warm up of the house

 

We only have a 60mm slab so can't coast as long through sub zero average temps.

Edited December 5, 2023 by Andehh

[HughF]

On 03/12/2023 at 12:19, JoeBano said:

Yesterday it was -3c all day here noticed my heat pump was short cycling a lot not really getting any heat downstairs either. My mixer on Ufh was set to 35c and flow temperatures on the heat pump were maxed out at 45c. Set to max on the mixer seem to stop the short cycling floors warmed up nicely. 

Assume you’ve got rads + ufh? If you’ve just got ufh, ditch the mixers…

[Jenki]

Jumping on this thread as it's opportune.

I've just got my Samsung Gen 6 running, I've got so much other stuff to do it's just working. 

My COP is rubbish.  Any quick tips on settings to assist?

Currently DHW is set to 43,as the showers / bath not working yet. So just hand washing and showering in the static 🥶.

I've set the temp on manual external thermostat to 18.5 .

90sqm UFH on manual at the moment the house is ok, great really, as we're working on it temp could be classed as too hot.

It's probably the worst time to look at settings as we've had negative temps over night for 3 or 4 days and some days hovering around 0.

But the COP is 2

 

I will get to spend time looking at this, just not yet, so any quick setup tips would be appreciated.

 

[Nick Laslett]

Folks, any thoughts about when it is too cold to commission an ASHP? @Jenki, @Conor, @JohnMo, @Nickfromwales

My gut feeling was no lower than 6°. I am going with anti-freeze valves. 

 

I am a few weeks away from being ready, no water in any of the system, just empty UFH loops. 
 

I am waiting on the electrician, I thought it best to have the machine connected before filling the system. The unit is still boxed up in the garage. 
 

 

[JoeBano]

On 07/12/2023 at 07:29, HughF said:

Assume you’ve got rads + ufh? If you’ve just got ufh, ditch the mixers…

Yeah rads upstairs. I would do but I’ve got an expensive wooden floor glued down, recommend it can’t go above 27c. I would rather keep it as fail safe incase my 2 port valve sticks open or the relay fail which shuts the heating 2 port valve in hot water mode. The hot water cycle will take this above 27c easily. 

[Jenki]

1 hour ago, Nick Laslett said:

Folks, any thoughts about when it is too cold to commission an ASHP? @Jenki, @Conor, @JohnMo, @Nickfromwales

My gut feeling was no lower than 6°. I am going with anti-freeze valves. 

 

I am a few weeks away from being ready, no water in any of the system, just empty UFH loops. 
 

I am waiting on the electrician, I thought it best to have the machine connected before filling the system. The unit is still boxed up in the garage. 
 

 

@Nick Laslett, I'm no expert, so can't comment, it's was probably 0 when I installed. And left it running overnight as it wasn't insulated very well.  I was using the UFH with the immersion so wasn't worried about water in the UFH plus the house hasn't dropped below 13deg once it was wind and watertight.

[JohnMo]

2 hours ago, Jenki said:

My COP is rubbish.  Any quick tips on settings to assis

Basically check you have immersion heaters kicking in.

 

Set a low flow rate and leave it to run. If you are heating a floor, it will take as much heat as you throw at it. Wind any room thermostats out the way see where is settles. Something like 28 deg flow. Then check to see if you are getting lots of start stopping, certainly for the first 24 hrs while it heat soaks you be getting very steady running.

[JohnMo]

2 hours ago, Nick Laslett said:

Folks, any thoughts about when it is too cold to commission an ASHP? @Jenki, @Conor, @JohnMo, @Nickfromwales

My gut feeling was no lower than 6°. I am going with anti-freeze valves. 

 

I am a few weeks away from being ready, no water in any of the system, just empty UFH loops. 
 

I am waiting on the electrician, I thought it best to have the machine connected before filling the system. The unit is still boxed up in the garage. 
 

 

Commissioning is very straight forward, the main thing is getting the air out the system before you start. Then set a low flow temp and press start. Initial run should have all thermostats set high, see you are getting warm water everywhere. Once running they look after themselves with out much or any input. After 24hrs take a note on we here room temps settle to and start to balance the system. And see what DHW does make sure the 3 way valve opens, you will need the G3 person to sign off the cylinder commissioning. 

 

As for temperature outside almost any temp is ok, but with the freeze valve you are best to get the system filled and running above zero. (Still not convinced by freeze valves)

[sharpener]

2 hours ago, Jenki said:

My COP is rubbish.  Any quick tips on settings to assist?

 

DHW settings:

• if tank is big enough run only once per day and ideally on offpeak electricity
• set DHW run time and anti-cycling time so as not to interfere unduly with heating
• target temp as low as you can tolerate, 43C sounds fine
• flow temp limit max 10deg higher (so 53C)
• hysteresis 10deg or more
• turn off legionella cycle if you are regularly using most of a tankful every day

Heating:

• Open all TRVs fully (if any) to start with, then use only as backstop for any rooms that overheat
• Run HP 24/7
• Increase setpoint by 1 or 1.5 deg during any periods of cheap electricity
• Setback 3deg (at most) at night and (if on Octopus Cosy) during evening peak electricity period.
• Use WC, check curve is not still on default setting (or worse, set up for a boiler), try 0.8 and reduce (or increase) no quicker than 0.1 every 24hours.
• Disable load compensation/room temp sensing to begin with
• Set max flow temp, min flow temp and OAT HP off threshold to sensible numbers.

 

[billt]

7 hours ago, Jenki said:

Jumping on this thread as it's opportune.

I've just got my Samsung Gen 6 running, I've got so much other stuff to do it's just working. 

My COP is rubbish.  Any quick tips on settings to assist?

Currently DHW is set to 43,as the showers / bath not working yet. So just hand washing and showering in the static 🥶.

I've set the temp on manual external thermostat to 18.5 .

90sqm UFH on manual at the moment the house is ok, great really, as we're working on it temp could be classed as too hot.

It's probably the worst time to look at settings as we've had negative temps over night for 3 or 4 days and some days hovering around 0.

But the COP is 2

 

I will get to spend time looking at this, just not yet, so any quick setup tips would be appreciated

 

 

You might be being a bit premature. The CoP of the Gen 6 isn't great at low temperatures, and if you are having defrosts they can knock 6-8% off the output. My overall CoP when the outside temp was freezing or below has been 2.4 to 2.6, but the SCoP so far is 3.77

[SuperJohnG]

Out of curiosity how is  everyone getting accurate CoP figures? 

[PhilT]

1 hour ago, SuperJohnG said:

Out of curiosity how is  everyone getting accurate CoP figures? 

Manufacturer's own software is pretty good. I have found input to be spot on based on verifying against meter readings. Not sure if it's possible to get any better than a calibrated software estimate for output, but mine looks reasonable compared to expectations (heat loss calcs etc.)

Edited December 8, 2023 by PhilT

[billt]

14 hours ago, SuperJohnG said:

Out of curiosity how is  everyone getting accurate CoP figures? 

 

I'm using the Open Energy Monitor heat pump monitor. https://shop.openenergymonitor.com/level-3-heat-pump-monitoring-bundle-emonhp/ The full kit is expensive, but I like to know what's going on and I'm not too sure that the readings given by the heat pump are accurate. It is very helpful when setting the system up.

 

If you want to look at other systems there are quite a few online at https://heatpumpmonitor.org/

[Nickfromwales]

On 08/12/2023 at 09:54, Nick Laslett said:

Folks, any thoughts about when it is too cold to commission an ASHP? @Jenki, @Conor, @JohnMo, @Nickfromwales

My gut feeling was no lower than 6°. I am going with anti-freeze valves. 

 

I am a few weeks away from being ready, no water in any of the system, just empty UFH loops. 
 

I am waiting on the electrician, I thought it best to have the machine connected before filling the system. The unit is still boxed up in the garage. 
 

 

Defo get the power on and be 100% ready to fill and keep it on! I commissioned one in the arse of last winter and it locked out a number of times and froze solid....was a right PITA tbf  Turns out it was just the flow rate set too high, but trying to reinstall the popped hoses with numb hands was 'pure bliss'  

[SuperJohnG]

On 08/12/2023 at 21:47, PhilT said:

Manufacturer's own software is pretty good. 

The Vaillant Arotherm unit doesn't give you the COP? it only provides info on energy yield as a total, then it gives power consumption for heating and DHW, but you can only figure out an overall COP not individual. 

 

My COP  was 2.74 last month. 1386kWh yield, 505 kWh power consumed. Seems like the COP isn't great. 

 

The WC I haven't messed with (largely as I don't know how) but it's fairly simple with no buffer, ASHP straight to the UFH which is a single zone.