degree minutes

[dfaz]

we have been commissioning a Nibe air to water heat pump installation,we had a few issues with operation and not coming back on as it should and going off while a heating demand was still calling,after talking through the issues with Nibe we came to the conclusion that the degree minutes setting was only -60 which was adjusted to -200 this seems to have cured the problem,although this was explained on our first training course I cant get my head wrapped around it,can anyone explain this in plain English?and does anyone else find these controls so overcomplicated?

Dave.

 

[Dodala]

Our Nibe Split has been in operation since last Friday and we have a similar problem, but it sound weird why a -200 would solve aresponse problem. My Nibe technichian explained me that the factory setting of -60 degree minutes means that the compessor would start in 6 minutes if it needs to increase by 10 degrees (in is not clear what 10 degree is - Celsius or something else?). Sorry for my English I am in Hungary....

We have a problem for the night set-back, maybe you can recommend something: we set back the temperature by 1 C for the night. The compressonr stops at 10 p.m. as the indoor unit realises that there is no heat demand. The problem is that it fails to start heating in the morning. The funny stuff is that it calculates the supply temperature correctly, so on the display you can see like: 30,4 (41,2), so it somehow knows the the heating should be on, be it starts heating only if I turn the room termostat up by 1-1,5 degree C. Nibe suggested to decrease the degree minute to -50 and increase the room compensation (menu 6.1) to 3. Nothing changed and Nibe said they can not solve the problem after checking the software and card version. This is quite strange to me and a simple 30 EUR thermostat would be better at the job I think.

 

[mysteryman]

You are probably using Celsius in Hungary.

If the weather is as mild there as it is here, it would be best to wait for colder times before altering too many settings.

The manufacturers of weather compensated heating equipment have been doing so and selling their kit for many decades now. It is reasonable to assume that they know their business. There will be all sorts of things in there, such as fuzzy logic which follows and to some extent anticipates trends in outside temperature.

It is true that with a simple room thermostat you may apparently get better, immediate, control, but it is nothing like as good as control by following changes in outdoor temperature. That is what alters the heat requirement of a building.

 

[dfaz]

On my original post it should have said the smo10 was set to -60,our system uses a separate weather compensation unit for the heating only so the Nibe unit is only controlling the buffer temperature,our issue was with the buffer tank temperature.the system is designed to give hot water priority feeding the top of the tank first the two vst 11 valves then motor over to feed the heating,so as the heated water is drawn from the tank the temperature drop continues and the heat pump should continue to run,it was explained to me that the degree calculation was being reached (ie-60) too soon so decreasing the figure to -200 would keep the pump on longer and not shut down when the hot water was satisfied.
Im sorry I have had no experience with Nibes own internal thermostat but one thing you might try you can adjust the heat curve by+ 1 factory setting is 9in menu 2.1 also if the weather is not very cold where you are at the moment you can adjust the offset curve to compensate check in the instructions for the smo 10.
It is possible that the weather compensation is delaying the start because it recognizes that by delaying the compressor start it can save energy without comfort loss hence when you turn up the stat the unit starts by adjusting the heat curve I think you will cure this.
I am quite a novice at this myself a bit like the blind leading the blind but hope this helps,i had to speak to three different Nibe technical operatives before I found someone who was very very good and understood the system inside out If you cant sort it out persevere with technical until you find someone to advise you correctly a poorly set up system could cost you a lot more to run than it should.

Dave

 

[dfaz]

Ok so I have had degree minutes explained to me AND I think i understand so here goes,the term relates to how many degrees in 1 minute acumulative.
if you take:
flow temperature setpoint T1
actual flow temperature TA
elapsed time in minutes T

If (TA) flow temp -(T1) temperature setpoint is higher than 0 the compressor will stop
If (TA)flow temperature -(T1)temperature setpoint is lower than 0 then it adds that to the degree minutes number it calculates every minute

SO after the first minute of running the flow temp -setpoint=-2 , degree minutes stores -2
2nd minute flow temp- setpoint=-3 , Degree minutes stores -3+-2 already in store= -5
3rd minute flow temp-setpoint=-3 , Degree minutes stores -3+-5=-8 after the acumulative amount reaches the the stored setting (ie -60) the unit will shut down .The unit will then start to receive plus figures calculating backwards as the temperature between flow and setpoint will be reversed .The heat pump will have a time delay to prevent the unit from firing too frequently(it uses more energy when starting) But the heat pump will still not come back on even when the time delay is exhausted unless the the degree minutes figure is back below the (in this case) -60 figure.It is a little difficult to understand but hope this helps.

Dave.