Hitachi Yutaki SCombi Heat Pump - Thermal Off's
I posted a few days ago to see if there were any owners of the Hitachi Yutaki SCombi Heat Pump. It seems it's a rare beast. I wanted to find out from other users their experience of this equipment. Having not found anyone, I thought there may be value in posting my issues. I have to add, I new to heat pumps and do not have assess to quality performance reporting statistics/equipment. So here goes:
System
2024 build bungalow
Moved in 9 months ago
200m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
3kw heat pump
50 litre buffer tank
Heat Pump Model No. (Indoor Unit ) RWD-3.0RW1E-220S-K
Heat Pump Model No.(Outdoor Unit) RAS-3WHVRP1
Comments
Unable to run the system 24/7 as the house gets to hot (24C overnight in the bedrooms)
I am only able to monitor the system (i) via a temperature probe fitted to the Gas Flow pipe into the indoor unit. (ii) via an energy monitor. The energy monitor shows when the heat pump switches on and off and when it performs a de-ice.
I have attached the result obtained of the gas temperature probe. The graph shows that there is "thermal off period" (that’s how Hitachi describe it), when compressor goes off – draws no power and then 8 minutes later the system conducts a de-ice. This thermal off period and then de-ice is so repeatable, different days, at different flow temperatures and different outside temperatures.
Why does the heat pump perform a thermal off period and then 8 minutes later a de-ice (and do it so consistently. Does this performance indicate anything wrong with my system?
I appreciate I may not have given all the info required, but this is a stating point. I have also attached an image of the internal unit
Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1
2024 build bungalow
Southern england
179 m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels
Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
Im not sure what you are monitoring but defrost is normally done by
switching off the fan
reversing the direction of refrigerant flow so the heat pump is operating to cool the house
thus using the heat stored in the circulating water to warm and defrost the evaporator
Hourly defrosts are not uncommon. In summary I cant see anything wrong with what yours is doing - is it causing a problem?
What flow temp are you running at/have you adjusted the weather compensation curve down until its as low as possible consistent with heating the house (difficult with current weather!)
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Posted by: @jamespaIm not sure what you are monitoring but defrost is normally done by
switching off the fan
reversing the direction of refrigerant flow so the heat pump is operating to cool the house
thus using the heat stored in the circulating water to warm and defrost the evaporator
Hourly defrosts are not uncommon. In summary I cant see anything wrong with what yours is doing - is it causing a problem?
What flow temp are you running at/have you adjusted the weather compensation curve down until its as low as possible consistent with heating the house (difficult with current weather!)
The fan does turn off, water from inside is then pumped in reverse, power is take to heat the water and then the fan and compressor runs. Takes about 5 minutes, so this seems OK.
I am currently running a fixed flow temperature, which I adjust dependant upon the weather. The minimum I can run is about 30C. When it really cold I would increase to 33C. The weather comp on the Hitachi system is not very good. The temperature probe on the Heat Pump detects the sun and also the increase in temperature from the de-ice cycle and causes the flow temperature to be erratic.
I am OK with a de-ice cycle ever hour, what I don't like is the thermal off 8 minutes prior to the de-ice. This happens every time irrespect of inside/outside/flow temperature.
Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1
2024 build bungalow
Southern england
179 m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels
Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
Posted by: @trebor12345The temperature probe on the Heat Pump detects the sun and also the increase in temperature from the de-ice cycle and causes the flow temperature to be erratic
Hitachi is sadly not alone. The OAT sensor should be in the shade and out of any influence from the heat pump itself. only some manufacturers do this!
Posted by: @trebor12345I am OK with a de-ice cycle ever hour, what I don't like is the thermal off 8 minutes prior to the de-ice. This happens every time irrespect of inside/outside/flow temperature.
Im guessing it might do this to minimise heat wasted by immediately flushing hot refrigerant through the cold part of the circuit. Thats only a guess however - it does seem a long time but the actual FT decrease in this period doesnt look that large. The exact logic is probably in the mind of the designer!
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
The first dip is the thermal off period where the compressor stops for 3 minutes and the refrigerant in the pipe from the heat pump to the internal unit drops a few degrees, the heat pump then starts up and runs for 5 minutes as can be seen by the slight rise in refrigerant temperature. (as measured by my temperature probe).
The second dip is the de-ice cycle where there is a significant drop in temperature as water is drawn from the buffer tank/underfloor.
Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1
2024 build bungalow
Southern england
179 m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels
Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
Posted by: @trebor12345The first dip is the thermal off period where the compressor stops for 3 minutes and the refrigerant in the pipe from the heat pump to the internal unit drops a few degrees, the heat pump then starts up and runs for 5 minutes as can be seen by the slight rise in refrigerant temperature. (as measured by my temperature probe).
Interesting. What does the water pump do during this.
I understand the compressor stopping, its will need to do that to switch from heating to cooling mode. 3 mins seems a reasonable time for this.
I don't understand whats happening in the 5 minute period though. Is it just some remaining refrigerant reaching your temperature probe, or some refrigerant being warmed by the inrush of water from the house (whats the water pump doing during this cycle?)? Basically is it still going through the 'change over' from heating to cooling, or is this in fact the early stage of defrost? Its not difficult to imagine that the change over does take some time to settle down if indeed it ever does during a defrost. In their original concept the change from heating to cooling happens only twice per season.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Posted by: @jamespaPosted by: @trebor12345The first dip is the thermal off period where the compressor stops for 3 minutes and the refrigerant in the pipe from the heat pump to the internal unit drops a few degrees, the heat pump then starts up and runs for 5 minutes as can be seen by the slight rise in refrigerant temperature. (as measured by my temperature probe).
Interesting. What does the water pump do during this.
I understand the compressor stopping, its will need to do that to switch from heating to cooling mode. 3 mins seems a reasonable time for this.
I don't understand whats happening in the 5 minute period though. Is it just some remaining refrigerant reaching your temperature probe, or some refrigerant being warmed by the inrush of water from the house (whats the water pump doing during this cycle?)? Basically is it still going through the 'change over' from heating to cooling, or is this in fact the early stage of defrost? Its not difficult to imagine that the change over does take some time to settle down if indeed it ever does during a defrost. In their original concept the change from heating to cooling happens only twice per season.
Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1
2024 build bungalow
Southern england
179 m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels
Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
In the 5 minute period the compressor is running, taking electrical power and producing heat. This, what Hitachi call a "Thermal Off" I might call a Short Cycle. But it happens with so much regularity, it's almost like it what supposed to happen.
So in summary, heat pump shuts down for 3 minutes, takes no electrical power, starts back up producing heat and then 5 minutes later starts its de-ice.
Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1
2024 build bungalow
Southern england
179 m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels
Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
Posted by: @trebor12345So in summary, heat pump shuts down for 3 minutes, takes no electrical power, starts back up producing heat and then 5 minutes later starts its de-ice.
Where does the heat during the 5 min period go, to the evaporator to de-ice or to the heating system (which makes no sense). Is the water pump running?
Posted by: @trebor12345But it happens with so much regularity, it's almost like it what supposed to happen.
I imagine that this is indeed the case, its unlikely to happen at random!
De-ice may have two phases or more(mine does). In the first phase that I know of the evaporator is heated by the refrigerant, getting its energy from the heating water. The fan is off. In the second short phase the fan starts up and blows off whats been melted (and maybe some more is melted during this phase), resulting in an impressive plume of steam.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Posted by: @jamespaPosted by: @trebor12345So in summary, heat pump shuts down for 3 minutes, takes no electrical power, starts back up producing heat and then 5 minutes later starts its de-ice.
Where does the heat during the 5 min period go, to the evaporator to de-ice or to the heating system (which makes no sense). Is the water pump running?
Posted by: @trebor12345But it happens with so much regularity, it's almost like it what supposed to happen.
I imagine that this is indeed the case, its unlikely to happen at random!
De-ice may have two phases or more(mine does). In the first phase that I know of the evaporator is heated by the refrigerant, getting its energy from the heating water. The fan is off. In the second short phase the fan starts up and blows off whats been melted (and maybe some more is melted during this phase), resulting in an impressive plume of steam.
The heat generated in the 5 minute period is with the pump on which goes to the manifold and floor.
My de-ice cycle is exactly as yours.
Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1
2024 build bungalow
Southern england
179 m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels
Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
Posted by: @trebor12345The heat generated in the 5 minute is with the pump on which goes to the manifold and floor.
Weird. This implies that the switch from heating mode to cooling mode is after this 5 minute period, in which case whats the 3 minute previous previous for? Somewhere there is probably an intelligible description of the hitachi defrost cycle.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Posted by: @jamespaPosted by: @trebor12345The heat generated in the 5 minute is with the pump on which goes to the manifold and floor.
Weird. This implies that the switch from heating mode to cooling mode is after this 5 minute period, in which case whats the 3 minute previous previous for? Somewhere there is probably an intelligible description of the hitachi defrost cycle.
I have no idea, to me there is no logic. There is no information on-line about this Hitachi system, so a bit of a loss.
Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1
2024 build bungalow
Southern england
179 m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels
Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
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