The dominant loud noise is the compressor or fan which you expect to be working at max during defrost.
The background rattle could just be ice, ice can make some funny noise! I have never listened to mine that close up during defrost its much nicer to be indoors enjoying the fruits of its labour. Another possibility is that something gets loose when its very cold. Unless someone tells you otherwise I would monitor but not worry. Have you tried sending that to Hitachi tech support?
How are you getting on with the data needed to set this system up so it (hopefully) warms the house with less intervention? I assume thats the end game!
This post was modified 4 weeks ago 2 times by JamesPa
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 dominant loud noise is the compressor or fan which you expect to be working at max during defrost.
The background rattle could just be ice, ice can make some funny noise! I have never listened to mine that close up during defrost its much nicer to be indoors enjoying the fruits of its labour. Another possibility is that something gets loose when its very cold. Unless someone tells you otherwise I would monitor but not worry. Have you tried sending that to Hitachi tech support?
How are you getting on with the data needed to set this system up so it (hopefully) warms the house with less intervention? I assume thats the end game!
Concerned about the noise and build up of ice. I believe that the evaporator should not be getting down to -23C, based on the algorithm. If I am interpreting the chart correct, at OAT -4C it should only get down to evaporator temperature of -8/10C.
Now producing the charts for you, have 2 days of data.
Have been in contact with manufacurer, awaiting reply.
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)
Concerned about the noise and build up of ice. I believe that the evaporator should not be getting down to -23C, based on the algorithm. If I am interpreting the chart correct, at OAT -4C it should only get down to evaporator temperature of -8/10C.
Maybe. It says 'outdoor evaporating temperature' (not refrigerant temperature) - its not clear what that means and the graph seems to define a region between the two hatched lines not an operation point, at least to me. So for example at OAT -4 the 'Outdoor evaporating temperature' could be any value <+4 and it would lie within the defrost region
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.
Concerned about the noise and build up of ice. I believe that the evaporator should not be getting down to -23C, based on the algorithm. If I am interpreting the chart correct, at OAT -4C it should only get down to evaporator temperature of -8/10C.
Maybe. It says 'outdoor evaporating temperature' (not refrigerant temperature) - its not clear what that means and the graph seems to define a region between the two hatched lines not an operation point, at least to me. So for example at OAT -4 the 'Outdoor evaporating temperature' could be any value <+4 and it would lie within the defrost region
You could be right in that it's a region between the 2 dotted lines. It's not clear to me what the chart really means, not my area of knowledge. Maybe someone who's an expert in this area can interpret.
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)
Maybe someone who's an expert in this area can interpret.
I think your concerns about abnormal refrigerant temperatures have been answered in this post.
Once we have some data we can look at whether the frequency of defrosts/short cycling are actually a problem (as opposed to a presumed problem). I have a hunch that switching over to weather compensated operation and possibly (but not definitely) operating for say 3 equally spaced periods of 4 hours each may deal both with your control problem and (if you have one) your cycling problem. The first is a must do, your house is simply never going to work based on room temperature control alone, whatever the heat source. The second is a maybe depending on the evidence.
The answers to some of the questions I asked are going to be key to working out the best set up, including in particular the one about 'how is the secondary pump controlled'? Also key to work out is what is causing the long 'thermal offs/flow temp reduction. The one you illustrated is not a normal cycling, its more like a thermostat with an unnecessarily large hysterisis or human intervention, with FT being maintained at 25C not by the heat pump, but by the slab. Hopefully the charts, together with your record of what you have done in terms of changing controls, will help ferret that out.
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.
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)
Water Temperature FIXED @ 31C. This temperature is a little warm in mild conditions and cooler in cold condition. But a happy medium.
My temperature sensors are placed on the pipes and wrapped in towels. They are a little in accurate in terms of precise temperature, because they are not direct contact probes.
Power consumption between 12:01am and 8:00am 12Kw.
Defrosts occurring every 46 minutes and at -23C evaporator temperature.
No setbacks and no human intervention.
There is a break in recording between 2/3pm due to power cut.
The off periods are: Hitachi Thermal Off Rule (short cycle) - Takes a shapshot of the water into the heat exchanger (Twi). Twi needs to drop by 4C to put demand back on.
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)
@trebor12345 Good data, will examine more closely before commenting. Do you have IAT for same period?
Can you clarify
what controls the secondary pump. Does it run 24x7 or switch on and off.
Also is the secondary fully open or are there zone valves etc?
What happened between 6pm and 8pm and after 10pm (is this what "The off periods are: Hitachi Thermal Off Rule (short cycle) - Takes a shapshot of the water into the heat exchanger (Twi). Twi needs to drop by 4C to put demand back on." refers to - if not what does it refer to - this isnt a short cycle its a long one!
Did the power cut also turn the heat pump off?
Have you any idea why the FT starts to rise before the defrost (Im presuming the rapid cycling is defrost) stops (about 3 cycles before)?
This post was modified 4 weeks ago 5 times by JamesPa
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.
@trebor12345 Good data, will examine more closely before commenting. Do you have IAT for same period?
Can you clarify
what controls the secondary pump. Does it run 24x7 or switch on and off.
Also is the secondary fully open or are there zone valves etc?
What happened between 6pm and 8pm and after 10pm (is this what "The off periods are: Hitachi Thermal Off Rule (short cycle) - Takes a shapshot of the water into the heat exchanger (Twi). Twi needs to drop by 4C to put demand back on." refers to - if not what does it refer to - this isnt a short cycle its a long one!
Did the power cut also turn the heat pump off?
Have you any idea why the FT starts to rise before the defrost (Im presuming the rapid cycling is defrost) stops (about 3 cycles before)?
The secondary pump runs all the time when there is a demand for heating and when in the Thermo Off situation.
Yes the power cut turned the heat pump off.
Yes the secondary manifold is fully open.
Yes the rapid cycling (15 off them) is the defrost cycling.
I have attached new chart which explains whats going on at defrost. Basically, following a defrost FT temperature rises, as evaporator ices up FT drops and then defrost starts. Hope this helps.
This image shows the Themo Off and On periods. Yes these are short cycles or as Hitachi say Thermo Offs. It's new software they installed back in the summer for me to overcome short cycling.
It can take anything from 2 to 4 hrs for heating demand to come back on following a Thermo Off.
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)
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)
Takes a shapshot of the water into the heat exchanger (Twi). Twi needs to drop by 4C to put demand back on.
Thanks for the extra info. A couple of questions and some comments
TWI being the buffer? or something else? If its the buffer 4C is a big drop given that the pipework is in a slab at 25-26C, hence a very long 'off'. Not sure what the implications of this are yet, just an observation at present.
The defrosts look normal except that the flow temp doesnt get back to 31. Yet the gradient of the rising edge is the same as immediately after the defrost and your expanded plot where you explain whats going on shows it level at the top not continuing to rise until the next defrost. Also the temp it reaches starts rising again for the last three of the defrost cycles, which wouldn't obviously be the case if something is 'wrong'.
Put simply it looks like something is controlling it to get only to 28. Are you absolutely sure that there is nothing in the setup that might be doing this eg low noise mode, overnight setback etc?
Could I ask you capture tonight also, its going to be warm hopefully above defrost temp so may rule out 'time of day' effects.
Water Temperature FIXED @ 31C. This temperature is a little warm in mild conditions and cooler in cold condition. But a happy medium.
I thought you had a problem controlling it to get the right temperature. Are you saying that fixed at 31C does produce the right house temp (within acceptable limits?)
This post was modified 4 weeks ago 2 times by JamesPa
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.
Takes a shapshot of the water into the heat exchanger (Twi). Twi needs to drop by 4C to put demand back on.
Thanks for the extra info. A couple of questions and some comments
TWI being the buffer? or something else? If its the buffer 4C is a big drop given that the pipework is in a slab at 25-26C, hence a very long 'off'. Not sure what the implications of this are yet, just an observation at present.
The defrosts look normal except that the flow temp doesnt get back to 31. Yet the gradient of the rising edge is the same as immediately after the defrost and your expanded plot where you explain whats going on shows it level at the top not continuing to rise until the next defrost. Also the temp it reaches starts rising again for the last three of the defrost cycles, which wouldn't obviously be the case if something is 'wrong'.
Put simply it looks like something is controlling it to get only to 28. Are you absolutely sure that there is nothing in the setup that might be doing this eg low noise mode, overnight setback etc?
Water Temperature FIXED @ 31C. This temperature is a little warm in mild conditions and cooler in cold condition. But a happy medium.
I thought you had a problem controlling it to get the right temperature. Are you saying that fixed at 31C does produce the right house temp (within acceptable limits?)
Twi (Temperature Water In) is Hitachi's term for water returning to the Heat Exchanger.
Remember, my temperature sensor are not metal probe type. So they do not accurately measure the precise temperature of the water. They give an indication of whats going on.
I have metal probes attached to the pipe work, and can confirm that the water does get to 31C. When it hits 31C we do go into Thermo Off.
Yes a set temperature of 31C works when cold and mild like today. (BTW no heating has been on since last night, house is still warm from the last heating cycle, tomorrows chart will explain).
Regarding the last 3 cycles. These are coming out of the defrost cycles, so the temperature rises. As mentioned above "Basically, following a defrost FT temperature rises, as evaporator ices up FT drops and then defrost starts". So never gets to the flow temperature.
The attached image shows the buffer tank with my probes attached (some in towels and insulation). Temperature displays on top of buffer.
I do not use any set backs. Not sure what low noise is, not seen it in the setup.
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)
