Modulation - what is your experience?

michaels

So my (space heating only) heat pump still doesn't run full time at 4C outside temp (about 50 mins on and 10 mins off) but does at 3C to maintain 21C inside when it is outputting about 5kw.

Once it does run continuously it does so at about 1.5kw so this is clearly the lowest it will go.  When it starts and stops it actually initially runs at 2kw before settling back.

The model is a Gen 2 (ie pretty old) LG Therma V, 12kw.  Our rated heat loss is 10kw but I think our realistic space heating demand is about 7kw max at -3C (with planned flow temp of 45C)

How does this compare to others experience. 
What is your heat pump model?
What outside temp gives you continuous operation?
What is the power draw at that minimum continuous output?

Thanks

matt_drummer

My 8kW Daikin Altherma 3 will run continuously at any any outdoor temperature I have ever tried it at.

Minimum average power consumption in a 24 hour period is around 350W

That is 24hours of heating at average outside temperature around 14c consumes  8.4kWh

michaels

matt_drummer said:

My 8kW Daikin Altherma 3 will run continuously at any any outdoor temperature I have ever tried it at.

Minimum average power consumption in a 24 hour period is around 350W

That is 24hours of heating at average outside temperature around 14c consumes  8.4kWh

So literally runs at 350w continuously?  Wow, much better than what my LG does.

matt_drummer

michaels said:

matt_drummer said:

My 8kW Daikin Altherma 3 will run continuously at any any outdoor temperature I have ever tried it at.

Minimum average power consumption in a 24 hour period is around 350W

That is 24hours of heating at average outside temperature around 14c consumes  8.4kWh

So literally runs at 350w continuously?  Wow, much better than what my LG does.

Not 350W continuously, it varies, sometimes more, sometimes less.

You can look at it.

Emoncms - app view

And others here

HeatpumpMonitor.org

NedS

Looks like we are very similar to you @michaels

We have a 12kW Samsung unit. The minimum electrical draw is somewhere around 800-900W, and the minimum output is around 4kW in mild weather where the COP is above 4 (for which our radiators need minimum flow temps of 32-33C to dissipate the heat generated).

We cannot run continuously until the outside temp falls below 5C (i.e, more heat being generated than the house requires).

Even then we turn off over night unless it's 0-2C, and then turn off at midnight and back on at 4am (we don't like it too hot for sleeping, so happy for the house temps to fall back overnight)

The other evening it was 2C outside (having been 2-5C all day), and the living room was holding a steady 20C at a flow temp of 32C.

In milder weather we just turn it on for an hour or two, and then off again once the house is up to temp and that works well for us and still gives good efficiency.

Today has been the coldest day of the year so far at around 2C all day, and we've been ticking along nicely with a flow temp of 33C drawing 1200-1400W with a COP of around 3.5 so putting out around 5kW of heat.

Electricity costs are 14.8p per kWh (Cosy), so with a COP of 3.5 we are paying around 4.2p per kWh equivalent for our space heating today which is still significantly cheaper than a 90% efficient gas boiler even in this cold weather (plus our solar generation today will completely cover our electrical usage for heating and DHW)

Netexporter

My 5kW Gen 6 Samsung was drawing about 2kW, first thing this morning, when the temperature was minus 6 degrees. It's now drawing about 1.6kW at just above freezing. Solar panels will soon be meeting all that load.

michaels

Netexporter said:

My 5kW Gen 6 Samsung was drawing about 2kW, first thing this morning, when the temperature was minus 6 degrees. It's now drawing about 1.6kW at just above freezing. Solar panels will soon be meeting all that load.

Do you know what its lowest continuous running draw is?

Netexporter

Seems to be around 5-600W.

The maximum I've seen is 4.4kW but that when it was in forced mode, whilst it was being commissioned, so I imagine about half that was the immersion heater.

NedS

The Heat Pump Monitor site has a table of minimum real world outputs for various heat pumps which you may find useful:

https://community.openenergymonitor.org/t/heatpumpmonitor-org-heat-pump-database-minimum-modulation-tests/29132

Hardly any manufacturers publish modulation data. The general rule of thumb is that most heat pumps will modulate down to around 25% of rated output. The reason they are limited to around 25% is that efficiency falls off a cliff if they modulate down much lower. They could modulate down to 10%, but you'd actually use more electricity for less heat output, hence each manufacturer will limit how low the compressor can modulate in an attempt to keep it within an acceptable operating window.

Be aware that 25% rule of thumb applies to the compressor hardware, not the headline sticker output of the unit. For example, my 12kW Samsung unit is really a 16kW unit that has been software limited to 12kW, so it's minimum output is 25% of 16kW (e.g, around 4kW), not 25% of 12kW (e.g, 3kW, which would have been much better for me).

Netexporter

Flow temperature is about 36 degrees at the moment. The radiators feel red-hot compared to the usual 30 degrees. Funny what becomes normal when you join the heat-pump folk.

michaels

NedS said:

The Heat Pump Monitor site has a table of minimum real world outputs for various heat pumps which you may find useful:

https://community.openenergymonitor.org/t/heatpumpmonitor-org-heat-pump-database-minimum-modulation-tests/29132

Hardly any manufacturers publish modulation data. The general rule of thumb is that most heat pumps will modulate down to around 25% of rated output. The reason they are limited to around 25% is that efficiency falls off a cliff if they modulate down much lower. They could modulate down to 10%, but you'd actually use more electricity for less heat output, hence each manufacturer will limit how low the compressor can modulate in an attempt to keep it within an acceptable operating window.

Be aware that 25% rule of thumb applies to the compressor hardware, not the headline sticker output of the unit. For example, my 12kW Samsung unit is really a 16kW unit that has been software limited to 12kW, so it's minimum output is 25% of 16kW (e.g, around 4kW), not 25% of 12kW (e.g, 3kW, which would have been much better for me).

Useful. I wonder if the max and min relate to output kw or input kw?