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  1. #1
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    Unhappy Altherma frequent compressor cycling



    Hi!

    I'm a new member here, so I would like to say hello to everyone first! I hope you can cope up with my writing since I'm not a native English speaker.

    I have a new house with a 6kW of heating power needed at -10°C ambient temperature, heated by an Daikin Altherma 8kW model (using Daikins swing compressor), driving a combination of underfloor heating and oversized radiators (connected on the same loop and using the same water temperature as the underfloor heating, always below 35°C ). I have no buffer tank. Indoor temperature regulation is done using Altherma's weather dependent water set point.

    Altherma can regulate heating power from 4kW to 8kW. House needs 4kW at 0°C outside, so at higher outside temperatures (like these days as it is 7°C to 10°C outside) it has to work in intervals. Here comes the problem with cycling :
    - altherma switches on for 2 minutes, starting with an higher compressor frequency and then gradualy reducing it, unitl it switches off at the end of this 2 minutes interval (since there is not enough heat demand).
    - it waits for 2 minutes (nothing is running, not even circulation pump)
    - switches on only the circulation pump for 2 minutes to read the water temperature - it is cold enough to cause it to start the compressor and starts the cycle again.

    So I have a compressor start every 6 minutes - it means 10 in an hour -> more than 200 per day!

    I believe that such a number of compressor starts is a recipe for heatpump failure, not to mention that it makes it difficult to maintain constant indoor temperature.

    I guess I could install an indoor temperature thermostat but I would prefer not to do it, because of the slow response from underfloor heating and low house temperature inertion (it is made of light prefabricated insulated elements) - it means that at quick outside temperature variations the indoor temperature would lag behind. Maybe a buffer tank would help but I have no space reserved for it (water unit is located under the staircase). I found no way to reduce the number of cycles using user modifyable settings.


    Is anyone else experiencing such problems with frequent starts/stops? Or am I just making an elephant out of a fly? Can a swing compressor withstand such a frequent cycling? I guess the same goes for pipes and heat excangers - is there a chance of early failure because of frequent pressure cycles? It is our first "real" heating season, heat pump was installed a year before (nov 2008), but rarely used since the house was not finished inside and we did not move in. I have another year of 3 year warranty period. I hope it does not break down the next day warranty expires. Can it last 10 years with such working regime?


    Kind regards



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    Re: Altherma frequent compressor cycling

    Hi,
    Does the system control on water temperature only? No room stats or zone valves etc.
    Does the system incorporate a bypass regulating valve? The min water volume must be at least 10L when valve is in bypass.
    Do you have commissioning data indicating the water flow rate?
    Have you checked the water strainer is clean?

    I would recommend installing a room thermostat, the weather dependant function can still be used.

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    Re: Altherma frequent compressor cycling

    Does the system control on water temperature only? No room stats or zone valves etc.
    Yes, the only control is Altherma's own weather dependent control.

    Does the system incorporate a bypass regulating valve?
    No. No bypass valves are installed.


    Do you have commissioning data indicating the water flow rate?

    No, the water flow was not measured, but it should be enough, since we managed to get the "not enough flow"
    error only when calibrating the flow through individual floor loops on first (lowest) pump speed with all the radiators "closed". In no other case this error occurs, so the flow rate should be high enough. The circulation pump has 3 possible settings - on highest and mid speed the water flow is high enough to cause hissing noise in the pipes (loud enough it can be heard throught the floor!), so I guess it is enough. The circulation pump is operating on middle speed, since at highest the noise realy gets "noticed".

    Have you checked the water strainer is clean?
    No, I talked to my installer and he said that because all piping is new the strainer should be clean. I have to say that I tried the running the circulation pump on each of three speeds, and after the system (water and floor temperature in function of the new flow rate) stabilises after about 10-12 hours , the behaviour is the same.

    I would recommend installing a room thermostat, the weather dependant function can still be used.
    As I said, I would prefer not to install a room thermostat, because the room thermostat signals the need for heating when room temperature has already fallen. By the time the underfloor heating builds up enough heat, I'm affraid it would be already quite cold inside the house because of the low thermal inertia of the house (I gets cold inside quickly), so I would prefer to have only weater dependant control, as it signals the need for heating as soon as it is needed. In this way the underfloor heating is "quick" enough to maintain constant inside temperature. I have to say that this system works remarkaby well with outside temperatures below 3°C since the working intervals become longer and power regulation is in effect.

    I guess the best solution would be to have a modfied firmware for the controller with a wider heating hysteresis, but I guess this is something only guys from Daikin can provide.

    I hope my answers explain the situation a bit.

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    Re: Altherma frequent compressor cycling

    I am not sure of your product, but principles do not change.
    I suggest that you have to much flow through your radiators (this is conterdictory to rads only) I suspect that the rads are unable to release the energy at at rate equal to the energy production. More flow through the floor is accebtable due to the ability of the floor to absorb larger amounts of energy compared to that of air. This should reduce the number of cycles, and I also think noise?? It should also smooth temp swings within the house (increased thermal storeage)
    More flow through the heat pump is always a benefit.

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    Re: Altherma frequent compressor cycling

    Hi!

    Thanx for suggestion - at first I had the same flow through all the pipes (checked with flow rate indicators on the manifolds), but this logic is flawed since hot water returns too quickly through radiators or the shortest floor loops. So I calibrated them in this way:
    - closed the valves (for the tested floor loop or radiator)
    - waited long enough for the radiator or floor to cool down (12-24 hours)
    - open the valve by 1 milimeter and then wait for the flow to have effect (to warm up the radiator or floor)
    - repeated the proces of opening of the valves by tiny bit and then waiting, until (in a few repetitions) the required heat output is obtained.

    In this way, there should be no short circuit of returnig hot water.

    I even tried with all the radiators closed, but the ciclying did not stop.

    However, this is my configuration:
    - 1. floor: 3x100m loops (living room, kitchen, dining room) + 2x50m loops (bathroom, hallway)
    - 2. floor: 1x75m loop (bathroom) + 3x Korado type 22 radiator of heating surface of 12m2 (aprox. the same as the room surface, so heat output is "almost" the same as with floor heating).

    Any other idea how to make it stop cycling?

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    Re: Altherma frequent compressor cycling

    So your unit, uses return water temp as the control method, the set point is adjusted in relation to the ambient.
    Lower ambient, higher set point.
    Higher ambient, lower set point.
    Is there a hysterises setting (differential)
    Is your house being at the right temp (It is working well apart from the short cycling)
    I am trying to get some feel for your system

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    Re: Altherma frequent compressor cycling

    So your unit, uses return water temp as the control method, the set point is adjusted in relation to the ambient.
    Yes, precisely. It is also written in the Service manual for the Altherma models 11kW - 16kW (my is 8kW, but the service manual for 8kW model does not explain the compressor frequency control). Maybe the algorithm for frequency control is the same, or it may be not the same. I got the manuals from the Daikin extranet

    Lower ambient, higher set point.
    Higher ambient, lower set point.

    Yes, current setpoints are 38°C at -10°C outside, 28°C at +15 outside.

    Is there a hysterises setting (differential)
    No, there is no user settable hysteresis. I guess this would be the solution to my problem.


    Is your house being at the right temp (It is working well apart from the short cycling)
    The temperature control works beautifully at low ambient temps, but it tends to overheat at high ambient temperatures because of fixed time intervals (2 minutes compressor operation every 4 minutes) and high starting compressor frequency, which gives too much heat.

    Thanx for your time.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by afternine View Post
    Hi!

    I'm a new member here, so I would like to say hello to everyone first! I hope you can cope up with my writing since I'm not a native English speaker.

    I have a new house with a 6kW of heating power needed at -10°C ambient temperature, heated by an Daikin Altherma 8kW model (using Daikins swing compressor), driving a combination of underfloor heating and oversized radiators (connected on the same loop and using the same water temperature as the underfloor heating, always below 35°C ). I have no buffer tank. Indoor temperature regulation is done using Altherma's weather dependent water set point.

    Altherma can regulate heating power from 4kW to 8kW. House needs 4kW at 0°C outside, so at higher outside temperatures (like these days as it is 7°C to 10°C outside) it has to work in intervals. Here comes the problem with cycling :
    - altherma switches on for 2 minutes, starting with an higher compressor frequency and then gradualy reducing it, unitl it switches off at the end of this 2 minutes interval (since there is not enough heat demand).
    - it waits for 2 minutes (nothing is running, not even circulation pump)
    I'm wondering why the circulation pump stops.

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    Re: Altherma frequent compressor cycling

    At the higher ambient, your units heating out put increases (2.5% per C).
    I would wasy we need to dampen the effect on the temp sensing probe. (without getting into the electronics)
    The probe needs to be removed from the pocket. (no longer in the direct water flow)
    Some form (an aluminium block, or a seal ed piece of pipe with some oil in) of mass needs to fixed onto the water pipe. The temp probe need to be fixed to this mass (opposite side to water pipe) This then need to be well insulated.
    you will get over and under shoot (short term), but a better averaged temp and reduction in short cycling.
    ( aliitle hard to sort problems, when somebody elese has written the software)

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    Re: Altherma frequent compressor cycling

    I have no experience with these particular systems, but it seems to me the pump should run 24/7 throughout the heating season.

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    Re: Altherma frequent compressor cycling

    @Gary
    This is another thing I also tried - I did force the circulation pump to work all the time (it is written in the user manual how to do it), but this did not improve the cycling. Since it did not matter, I put it back to default operation (on/off). Maybe they switch it off to save electricity, but I guess it only strains the pipes with flow starting/stopping.

    @mad fridgie
    As far as I could see, the Altherma has the temperature probes on the tubes, not directly in the waterflow - it has an insulation sleeve over the tube and a wire going in between the tube and the inslulation. I would post a picture, but the forum does not let me post html links yet.

    But I think your suggestion might work! I have to talk to my installer about this modification (I guess someone could tell without a doubt that sensor has been tampered with) so I don't get my warranty void.

    Is it possible that such modification (delayed reading of correct return flow temperature) breaks something (i.e. compressor overload or something similar)???

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    Re: Altherma frequent compressor cycling

    Your are not running the machine at extremes, so slight overshoot will not have an effect the the running gear (comp, etc)
    Your present probe is position is effectively is in the flow. (quick reaction)
    a simple test, get some aluminium foil (or foil tape) add aprox. 40mm around the pipe, add probe at about 30mm. (add some insulation old socks just for test)

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by afternine View Post
    @Gary
    This is another thing I also tried - I did force the circulation pump to work all the time (it is written in the user manual how to do it), but this did not improve the cycling. Since it did not matter, I put it back to default operation (on/off). Maybe they switch it off to save electricity, but I guess it only strains the pipes with flow starting/stopping.
    I wouldn't expect it to improve right away. The water would need to circulate for a while, but would eventually even out the temps.

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    Re: Altherma frequent compressor cycling

    @Gary
    I had it on 24/7 for about 45 days - I knew it would take a while to get things in balance, but sadly it did not improve the cycling.

    @mad fridgie
    You surely got me fired up, I will take a look tomorrow how to try it out (it's almost midnight here and everyone is already sleeping, so makeing noise this very moment is not an option).

    On the other hand, I guess I run the machine at full power sometimes - I'm sorry I did not tell it before, but Altherma is used for heating the hot sanitary water, too. When heating the HSW, the water temperature gets to about 50°C, which is Alterma's max water temperature. Is there anything that can go wrong because of the modification when heating HSW?

    Right now I try to reduce cycling by using the built in timer and alternating intervals with lower temperature and higher temperature than it would be normal. Needless to say that this is not the desired operating mode.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by Gary View Post
    I wouldn't expect it to improve right away. The water would need to circulate for a while, but would eventually even out the temps.
    This maybe true for fixed water temps, but these system the temps change.
    If you imagine that the house heat exchangers (rads and underfloor) are added together and have a total total rating of 0.3Kw/C (based on linear, not quite true put good enough) ie; house 20C water 25C heat released would be 1.5kw
    So when cold outside, water is 38C so heat rejected into the house is 5.4kw (this would balance roughly with units performance all fine)
    When mild ambient (15C) water is at 28C, so heat rejected 2.4Kw, but heat output would be at least a good 10kw. the nett effect si the the water warms very quickly. Unit turns off, but does not have enough time to change the thermal mass temp with in the house, so short cycling.
    Many ways to fix in design, but trying to find one without major mechnical or electronic changes.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by mad fridgie View Post
    This maybe true for fixed water temps, but these system the temps change.
    If you imagine that the house heat exchangers (rads and underfloor) are added together and have a total total rating of 0.3Kw/C (based on linear, not quite true put good enough) ie; house 20C water 25C heat released would be 1.5kw
    So when cold outside, water is 38C so heat rejected into the house is 5.4kw (this would balance roughly with units performance all fine)
    When mild ambient (15C) water is at 28C, so heat rejected 2.4Kw, but heat output would be at least a good 10kw. the nett effect si the the water warms very quickly. Unit turns off, but does not have enough time to change the thermal mass temp with in the house, so short cycling.
    Many ways to fix in design, but trying to find one without major mechnical or electronic changes.
    I would tend towards major changes.

    For starters, I would add a separate pump for the rads and run it off a room thermostat.

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    Re: Altherma frequent compressor cycling

    You explained it very well. I thought that a producer like Daking would have sorted such things out, but I guess they did overlook this situation. BTW, is there any way to get in touch with Daikin and let them know about this problem?

    By using aluminium foil -> you mean the foil my wife has in the kitchen for wrapping food? I guess it takes many wraps to make it 40mm thick!

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    Re: Altherma frequent compressor cycling

    I suspect when you do your domestic hot water (HSW), run time will be of some length, so dampening is reduced, and overshoot is reduced, this is not a major!

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by afternine View Post
    You explained it very well. I thought that a producer like Daking would have sorted such things out, but I guess they did overlook this situation. BTW, is there any way to get in touch with Daikin and let them know about this problem?

    By using aluminium foil -> you mean the foil my wife has in the kitchen for wrapping food? I guess it takes many wraps to make it 40mm thick!
    Yes just ouy of the kitchen, Fold foil into a saugage first (to make fatter) less times to wrap, need not be perfect!

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    Re: Altherma frequent compressor cycling

    Yes, heating HSW takes 40+ minutes, so I guess dampening would not be an issue.

    @Gary
    I would really like to try the alternatives which require no major $ or € or ...

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    Re: Altherma frequent compressor cycling

    OK, I'll see if I can try the "sausage" fix... I'll try to wrap it up tight first to get good thermal conductivity and small dampening and if it does not help then loose it up to make dampening bigger.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by afternine View Post
    OK, I'll see if I can try the "sausage" fix... I'll try to wrap it up tight first to get good thermal conductivity and small dampening and if it does not help then loose it up to make dampening bigger.
    This is a bit trail and error, at this stage just proving that it works (it will, in a fashion) It is alittle easier for me when I can touch and feel, so can only give basic indications.
    Once proved you install company should be able to knock something up, that is a bit more prescise.
    Go to bed, I hear your wife call!

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    Re: Altherma frequent compressor cycling

    He he, wife already sleeps for about 2 hours .

    I will post as soon as I get some results. I just hope not to break something - you know - just finished the house and moved in - so no surplus of cash at the moment for a replacement heat pump.

    Is there any way to contact Daikin and get this fixed as it should be - with software upgrade? I can try writing to support@daikin.com but I guess it is a long shot.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by mad fridgie View Post
    Your are not running the machine at extremes, so slight overshoot will not have an effect the the running gear (comp, etc)
    Your present probe is position is effectively is in the flow. (quick reaction)
    a simple test, get some aluminium foil (or foil tape) add aprox. 40mm around the pipe, add probe at about 30mm. (add some insulation old socks just for test)
    Mad fridgie,
    I understand your thought process but there is a couple of problems with it:
    1/ The unit has 3 water sensors (+1 in DHW tank)
    2/ The sensor is also used to calculate required outdoor capacity, so reducing the sensor temp will increase capacity.

    Quote Originally Posted by mad fridgie View Post
    I suspect when you do your domestic hot water (HSW), run time will be of some length, so dampening is reduced, and overshoot is reduced, this is not a major!
    The DHW tank has an idependant sensor and a larger dead band which is adjustable.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by VRVIII View Post
    Mad fridgie,
    I understand your thought process but there is a couple of problems with it:
    1/ The unit has 3 water sensors (+1 in DHW tank)
    2/ The sensor is also used to calculate required outdoor capacity, so reducing the sensor temp will increase capacity.


    The DHW tank has an idependant sensor and a larger dead band which is adjustable.
    I do not know the product, good that you have practical experience.
    We are not reducing the sensor temp, but reducing the reaction time.
    I suspect (but could be wrong) when these start up, that after a short period, they ramp to full speed, (possibly for a number of reasons) when getting close to set point unit will ramp down (more than likely many smarts controlling) i did state that the ubit will under and over shoot.
    This is a compremise,.
    maybe there are more changes to be made in the software at a higher level than the operator can access. One presumes he has already contacted his specialist.

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    Re: Altherma frequent compressor cycling

    Hi guys, I'm not in bed, yet...

    I did contact my installtion specialist and he did measure the compressor frequency - fast start then slowing down. He said everything is OK and that I have to live with it .

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by afternine View Post
    Yes, current setpoints are 38°C at -10°C outside, 28°C at +15 outside.

    The temperature control works beautifully at low ambient temps, but it tends to overheat at high ambient temperatures...
    This would seem to indicate that 28C@15C is too high.

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    Re: Altherma frequent compressor cycling

    Originaly it was set to 25°C at +15°C outside (it can not be set lower than 25°C) but I also got overheating. I tried to rise it up a bit to lenghten the working interval and (hopefully) the stop interval, too. Sadly, it didn't work out this way, and I left it on 28°C, as it didn't do any difference. I will put it back to 25°C.

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    Re: Altherma frequent compressor cycling

    How is it going?

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    Re: Altherma frequent compressor cycling

    I know that you are concerned about compressor starts but a brief read of the manual indicates that the room sensor, if fitted, is designed to stop overheating by switching the system off.

    Perhaps this may be worth investigating as the outdoor unit is oversized for the heat load.
    Brian - Newton Abbot, Devon, UK
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    Re: Altherma frequent compressor cycling

    Hi!

    While rereading the entire thread again, the reply from Gary (... This would seem to indicate that 28C@15C is too high ...) got me thinking for the milionth time:

    I can not set lowest setpoint lower than 25°C (factory setting, although there is a setting 9-01 "Heating set point lower limit. which I set to 15°C, so it should let me set the low setpoint lower than 25°C, but it does not). Than I got the idea: 25°C is at 15°C outside - maybe I can "move" the 15°C outside - indeed I could set it, I set it to 11°C - this is equivalent to 22,5°C at 15° outside. In this way I can lower the low end of the heating curve.

    Then I removed the units cover, set the circulation pump to "always on" and waited for a couple of hours - and I have a little difference! Today it was cloudy with almost constant temperature between 9°C and 10°C and the compressor makes 2 to 3 cycles (2 minute on, 4 minutes off), then "sleeps" for about 8 minutes (skips 1 to 2 cycles), then it repeats 2 to 3 cycles, sleeps for 8 minutes... I guess it is some improvement, although really not much.

    While the cover was off, I took a look at thermistors: there are 4 thermistors:
    - inlet return water
    - outlet water heat exchanger
    - refrigerant liquid side heat exchanger
    - outlet backup heater

    Here is a copy/paste excerpt from the Service manual regarding frequency control:

    3.3 Frequency Control
    Outline
    Frequency will be determined according to the difference between water and set temperature.

    The function is explained as follows:
    How to determine frequency.
    Frequency command from a hydro-box (the difference between the water temperature and the
    temperature set by the remote controller).
    Frequency command from a hydro-box.
    Frequency initial setting.
    PI control.


    Determine command frequency
    Command frequency will be determined in the following order of priority:
    Limiting frequency by drooping function
    Input current, discharge pipes, low Hz high pressure limit, peak cutting, freeze prevention, fin
    thermistor temperature.
    Limiting defrost control time
    Forced cooling
    Indoor frequency command

    Determine upper limit frequency
    Set a minimum value as an upper limit frequency among the frequency upper limits of the following
    functions:
    Compressor protection, input current, discharge pipes, Low Hz high pressure, peak cutting, freeze
    prevention, defrost.

    Determine lower limit frequency
    Set a maximum value as an lower limit frequency among the frequency lower limits of the following
    functions:
    Four way valve operating compensation, pressure difference upkeep.

    Determine prohibited frequency
    There is a certain prohibited frequency such as a power supply frequency.


    Indoor frequency command (∆D signal)
    The difference between the outlet water temperature and the temperature set by the remote controller will be taken as the “∆D signal” and is used for frequency command.

    Frequency initial setting
    When starting the compressor, or when conditions are varied due to the change of the room, the frequency must be initialized according to the total of a maximum ∆D value of the hydro-box and the Q value of the hydro-box.
    Q value: hydro-box output determined from hydro-box.


    PI Control (determine frequency up/down by ∆D signal)
    P control
    Calculate ∆D value in each sampling time (20 seconds), and adjust the frequency according to its
    difference from the frequency previously calculated.

    I control
    If the operating frequency is not change more than a certain fixed time, adjust the frequency up
    and down according to the ∆D value, obtaining the fixed ∆D value.
    When the ∆D value is small...lower the frequency.
    When the ∆D value is large...increase the frequency.

    Limit of frequency variation width
    When the difference between input current and input current drooping value is less than 1.5 A, the
    frequency increase width must be limited.

    Frequency management when other controls are functioning
    When frequency is drooping;
    Frequency management is carried out only when the frequency droops.
    For limiting lower limit
    Frequency management is carried out only when the frequency rises.

    Upper and lower limit of frequency by PI control
    The frequency upper and lower limits are set depending on hydro-box.
    When outdoor unit low noise or quiet commands come from hydro-box, the upper limit frequency
    must be lowered than the usual setting.

    If I'm right, the main thing that regulates the compressor frequency is the ∆D, which is "the difference between the outlet (which oulet???? heat exchanger or floor heating manifold) water temperature and the temperature set by the remote controller". Maybe someone can see some other way to lenghten the cycles.

    I guess the only thing that would fix cycling is "sausage fix" or updated software.

    Before atempting the sausage fix I will contact my installer and discuss it with him.

    I have no room sensor fitted in the house. As for the oversized outdoor unit - every Altherma under the 8kW range has minimum power output of 4kW - even the smallest 6kW unit (so I guess it is not much of an inverter). The only difference between units in 6 - 8 kW range is max compressor frequency. I don't know about bigger Althermas (11-16kW range) as they don't have stated minimum power output and have different type of compressor (scroll).

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    Re: Altherma frequent compressor cycling

    Six cycles per hour is widely considered acceptable.

    I would be more concerned with the overheating in milder weather.

    And I would think twice before messing with the frequency controls.

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    Re: Altherma frequent compressor cycling

    Six cycles per hour is widely considered acceptable.
    OK, but what would be an optimal number of cycles in such mild conditions? What number of cycles per hour would you like to see if it was your heatpump?


    I would be more concerned with the overheating in milder weather.
    With the new lower setpoint setting I hope it is resolved. As for what I could see today I think overheating won't be an issue any more.


    And I would think twice before messing with the frequency controls.
    That's why I want to talk to my installer - I do not want to fry something and be left without warranty.

    Today I heard one possible reason why is such cycling designed - Althermas in 6-8kW range do not have a crankcase heater - could be power cycling needed to keep the compressor from cooling down too much???

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by afternine;179629OK
    , but what would be an optimal number of cycles in such mild conditions? What number of cycles per hour would you like to see if it was your heatpump?
    Without a buffer, it either runs more often or has wider temp swings... pick your poison. Six per hour is acceptable.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by Gary View Post
    Without a buffer, it either runs more often or has wider temp swings... pick your poison. Six per hour is acceptable.
    Agreed,
    I think this must be a well insulated house (or very small), and a quick acting system.

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    Re: Altherma frequent compressor cycling

    I'd prefer a little bit wider temp swings and a compressor that runs for 20 years. As it is now, I hope it runs for 10 years.

    The house is a 2 store high light prefabricated construction with 20cm of isolation on walls. It does not need much heating power, but once you switch heating off it cools down rather quickly because of low mass. This is the reason I opted for underfloor heating - needed to have a mass that keeps temperature stable. I would not have installed radiators, but wife insisted not to have ceramic tiles in bedrooms.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by afternine View Post
    I'd prefer a little bit wider temp swings and a compressor that runs for 20 years. As it is now, I hope it runs for 10 years.

    The house is a 2 store high light prefabricated construction with 20cm of isolation on walls. It does not need much heating power, but once you switch heating off it cools down rather quickly because of low mass. This is the reason I opted for underfloor heating - needed to have a mass that keeps temperature stable. I would not have installed radiators, but wife insisted not to have ceramic tiles in bedrooms.
    Play with the sausage, this will give the swing (under/over shoot)

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by afternine View Post
    I can not set lowest setpoint lower than 25°C (factory setting, although there is a setting 9-01 "Heating set point lower limit. which I set to 15°C, so it should let me set the low setpoint lower than 25°C, but it does not).
    This is to stop "over condensing" and liquid return to the compressor. When the water temp is 16C or below, the Hydrobox will engage the back up heater to raise the water circuit temp before allowing the compressor to run.

    regulates the compressor frequency is the ∆D, which is "the difference between the outlet (which oulet???? heat exchanger or floor heating manifold)
    It is the outlet from the Hydrobox as there is no sensor on your underfloor manifold.
    The compressors do not need a crankcase heater as they pass a small current through the windings during the off cycle, to warm the oil.

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    Re: Altherma frequent compressor cycling

    Frank, thax for clarifying things.

    It is the outlet from the Hydrobox as there is no sensor on your underfloor manifold.
    He he... sure there is no sensor on manifold

    Now I'm in doubt if the "sausage fix" would work - we were talking about delaying readings from the inlet return water thermistor of the heat exchanger (thus prolonging the diference between the return flow and the setpoint), not the outlet (difference between momentarily achieved water temperature and set point).

    Now the question is: should the sausage fix be applied to the outlet water heat exchanger thermistor, too? Maybe only to the outlet thermistor? The Service manual is not clear about this - all it says is "the difference is computed between the outlet and setpoint".

    I know this is becoming a little bit silly (delaying readings here and there), but I would like to grasp the theory correctly.

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    Re: Altherma frequent compressor cycling

    This is making sense, and makes worse. The higher the ambient the hot water coming out.
    When you have the pump turning on and off, how long is the pump on after the comp turns off?

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    Re: Altherma frequent compressor cycling

    When you have the pump turning on and off, how long is the pump on after the comp turns off?
    The circluation pump switches off at the same time as the compressor. From that moment outside fan runs for another minute, but the circulation pump sleeps for 2 minutes. Then the circ. pump goes on for 2 minutes to get the water temperatures right. Ater this second 2 minutes interval, the compressor starts.

    Right now I have the circulation pump on "always on" setting.

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    Re: Altherma frequent compressor cycling

    I need to find out when the comp and pump turns off, what then turns the pump back on.
    A; Just temp setting
    B: Pump pulses every so oftern to ensure that probe is reading the right temp.
    To test set pump back to on/off mode.
    Adjust set point high, run until water temp is high, then turn to low set point.
    All should turn off, watch pump, how long before pump comes back on?

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    Re: Altherma frequent compressor cycling

    I need to find out when the comp and pump turns off, what then turns the pump back on.
    The circulation pump goes on 2 minutes after the compressor stopped, and stays on (it does not turn off until next compressor stop)

    Adjust set point high, run until water temp is high, then turn to low set point. All should turn off, watch pump, how long before pump comes back on?
    I currently do this strategy (high temp then low temp) with timer (runs for 3 hours at the weather dependent set point +3°C , then for 5 hours at -5°). This way I use underfloor heating as buffer tank for radiators (room temperature does not swing more than 0,5°C) and somewhat lower the number of compressor starts. The circluation pump runs as described above. Compressor start is triggered when water gets cold enough for the current setpoint.

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    Re: Altherma frequent compressor cycling

    OK, not what I wanted to hear!
    Increase water flow would help, but noise is a problem.
    The foil will still dampen the effect. (not quite as good as on the return)
    Set controller back to original settings, but have set point at 25 not 28. (at 15 ambient)
    Have ago! It should increase run times and increase of times.

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    Re: Altherma frequent compressor cycling

    I'm getting confused with the water sensor positions, it's me, don't worry

    On an underfloor system using a heating boiler the normal control would be aiming for a set point temperature on the flow to the manifold.

    The set point would be controlled by a mixing or diverting valve on the underfloor water circuit.

    So the Altherma is trying to achieve set point temperature by modulating the compressor speed whilst the set point is being modulated itself by the weather compensation software in the system.

    Also, if the pump stops with the compressor off mode then whenever the pump starts, in a temperature sampling, then is it monitoring the temperature of the water returning from the underfloor system or is it checking the temperature from the hydrobox?

    It seems to me that the underfloor loops are not maintaining a stable temperature (maybe that's the way it is designed?) which goes against the design of underfloor heating; correct me if I'm wrong here.

    If we assume that a heating cycle has completed and the pump has shut off then, with your low heat retention, the water in the pipe loops will begin to cool quite quickly.

    The pump kicks in to check the system status and gets a slug of overcooled water. So the system starts up with the compressor heading for maximum capacity to compensate.

    I think that you should keep the pump running to provide a more steady load on the controls.
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

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    Re: Altherma frequent compressor cycling

    I sort agree Brian, I would not control a system as descibed, but what do I know.
    With how it seems set up, and the temp settings, there simply is not enough run time to introduce energy energy into the underfloor (thermal storage), so regardless if the pump runs or cycles, water temp will fall quickly.
    This system also has rads, so heat is lost very quickly from these (no thermal mass)
    There seems to be no method of adjusting diff or dead band on these units.
    All problems can fixed with $$$$
    Normally, i control on return water temp (cold into the heat pump) and have room control via a stat in the concrete (Not in the air, no good for underfloor heating with a heat pump)
    Increaseing the flow through the cond, would reduce the TD between water in/out and would introduce more energy into the floor, and make the system more stable, but at high flow noise seems to be a problem.

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by Brian_UK View Post
    So the Altherma is trying to achieve set point temperature by modulating the compressor speed whilst the set point is being modulated itself by the weather compensation software in the system.
    Exactly.

    Quote Originally Posted by Brian_UK View Post
    Also, if the pump stops with the compressor off mode then whenever the pump starts, in a temperature sampling, then is it monitoring the temperature of the water returning from the underfloor system or is it checking the temperature from the hydrobox?
    It has a termistor before and after the heat excanger in the hydrobox. While the compressor is off, the water passing through heat excanger is not heated, so both thermistors read the same value. Altherma displays on the control panel the temperature that is on the heat exchanger outlet, so when compressor starts you can see water temperature raising, but you can not see the water temperature coming from the manifold (return flow) any more.

    Quote Originally Posted by Brian_UK View Post
    It seems to me that the underfloor loops are not maintaining a stable temperature (maybe that's the way it is designed?) which goes against the design of underfloor heating; correct me if I'm wrong here.
    The underfloor loops keep rather stable temperature, since there is 15cm of insulation beneath the loops, and they are covered with 6cm of concrete, on which ceramic tyles are laid. The water from radiators is joined (mixed) with water from underfloor loops before going to heatpump. As far as I could observe it looses (the mixed water) about 1°C in 2 hours. This is not an exact measurement.

    Quote Originally Posted by Brian_UK View Post
    I think that you should keep the pump running to provide a more steady load on the controls.
    That's why I set it to "alwasy on".

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    Re: Altherma frequent compressor cycling

    Quote Originally Posted by mad fridgie View Post
    Increaseing the flow through the cond, would reduce the TD between water in/out and would introduce more energy into the floor, and make the system more stable, but at high flow noise seems to be a problem.
    I'm wondering if decreasing the water flow wouldn't stretch the run time and thus lengthen the cycles.

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    Re: Altherma frequent compressor cycling

    Increaseing the flow through the cond, would reduce the TD between water in/out and would introduce more energy into the floor, and make the system more stable,
    There was an idea to switch the pump to slowest speed to let the water to really cool down before returning to heat pump, thus increasing dT. Needless to say that did not work. Then we tried on max speed for a entire day to let it stabilise - also did not work.

    but at high flow noise seems to be a problem.
    yes, on max speed it is unaceptable, so it is runinng on middle speed always on.

    There seems to be no method of adjusting diff or dead band on these units.
    This is the source of "all evil"

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    Re: Altherma frequent compressor cycling

    I'm wondering if decreasing the water flow wouldn't stretch the run time and thus lengthen the cycles.
    It seem that at min speed the all the heat generated can not get transfered to water quickly enoug, so the compressor stops.

    It seems that even at max speed the heat can not get transferred quickly enoug from water through pipes to concrete to cool it down to have a large enough temperature difference on return. On the other hand, when concrete is heated enoug - it can not accept any more heat (energy is transfeered only from higher temp to lower temp - when there is no heat difference, there is no energy transfer, so a wider band would be needed.

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