degree minutes?

[dfaz]

i'm a heating engineer by trade and we are getting more involved with heat pumps as demand grows.It doesnt matter how many training courses i go on there is no substitute for hands on,so I prefer to struggle on untill i know what and how things work.I,m struggling to get my head around degree minutes and how it affects the heat pump.The unit I have been dealing with is a Nibe air to water unit which would not come back on untill it saw -60 degree minutes it was adjusted to -200 in the controll unit,it now works ok.well the problem is solved but I dont understand why,can someone explain in plain english to someone who is a novice when it comes to heat pumps.Hope this makes sense to some of you technical bods.
Thanks in advance.

Dave.

[mad fridgie]

No idea about Nibe, but lived in lancaster/morecambe. Talk to Jason from Absolute Cooling, he is in Heysham, nice guy.

[mad fridgie]

Thanks Frank!!

[frank]

You're welcome :D

[nike123]

Internal equipment:

We haven't discussed hot water yet in any detail.

A heatpump usually runs at lower temperatures than conventional boilers. When heating hot water it needs to get a bit warmer, so the CoP lowers during this process. Some heatpumps use mains immersion heaters to top up hot water, which is fine in countries where hydro and nuclear generated electricity is cheap, renewable and plentiful. In the UK our electricity is none of these things.

Generally speaking, a heatstore is needed inside the property. This takes the form of a large water cylinder, which is a large buffer mass of heat.

What is the heatstore for?

Firstly, to keep up the 'degree minutes' of the heatpump. Secondly, to provide a means of supplying hot water.

Fixed rate compressors in heatpumps are most efficient when operating for long periods. A cycling heat pump compressor will use more energy (starting surges etc) and have a significantly reduced operating life. Thus systems are designed to maximise 'degree minutes'.

So heatpump specifiers and designers usually need to provide a large buffer store of water from which Underfloor or radiators are attached, and typically a hot water cylinder will be wholly submerged inside this tank too. This allows the heatpump to run on longer without cycling.

http://www.hwch.co.uk/boilers.html

[csdome]

i'm a heating engineer by trade and we are getting more involved with heat pumps as demand grows.It doesnt matter how many training courses i go on there is no substitute for hands on,so I prefer to struggle on untill i know what and how things work.I,m struggling to get my head around degree minutes and how it affects the heat pump.The unit I have been dealing with is a Nibe air to water unit which would not come back on untill it saw -60 degree minutes it was adjusted to -200 in the controll unit,it now works ok.well the problem is solved but I dont understand why,can someone explain in plain english to someone who is a novice when it comes to heat pumps.Hope this makes sense to some of you technical bods.
Thanks in advance.

Dave.
Hi
I am a serviceman in Hungary.
I know how is working the Nibe's Degree minutes. I think i can help you , if you want.
What is the type of yr machine?
the initial setting is in the control :
step1 : -60 dm
the unit calculate the DM. in ewery minutes. this number is the actual dm. That you can adjust, if the actual dm is lower than the setting eg. -200, the compressor is starting.

Ask me if you have any question

[dfaz]

Hi there
The Nibe unit is a 2015 11kw with an smo 10 controler.the buffer tank is a vpas 300/450 300hot water 450 buffer conected to solar,its set up as floating condensing with 2 vst11 3port valves controlling hw priority and heating i just need to understand how the degree minutes controlls and adjusts etc in laymans terms as plain as poss thanks Dave.

[csdome]

Ok. sorry of my wrong english
So. the degree minute is a calculated number
it makes by 3 things:
1. flow temperature setpoint . bee this T1
2. actual flow temperature bee this Ta
3. elapsed time in minutes. bee this t

2015 is only heating, with 1 compressor
if the unit is working it is calculate the difference
if Ta-T1 is higher than 0 the compressor is stop
if Ta-T1 is lower tha 0 then storage it to DM number
it mage ewery minutes.

so example
in first minute Ta-T1= -2 degrees celsius then store -2 in DM counter.
in second minute Ta-T1 = -3 then store -3 to DM counter now the DM is (-2+-3)=-5
the 3.rd minute the difference is -3 too then DM= (-5)+(-3)=-8
after some minute the dm value lowr tha the starting setting. then the compressor is running.

(the starting setting you can adjust in menu 9.1.1 between 0 to -120. factory default is -60)

.. and the unit is calcolate away the degree minutes to the zero. then the compressor is stopping.

( you can see and adjust the actual calculated DM's in menu 2.8. )

That's it

[dfaz]

your English is not bad and I understand more than I did thanks for taking the time to reply

Dave

[Dodala]

Magyarul is irhatod a választ kösz.
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.

[csdome]

Magyarul is irhatod a választ kösz.
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.
you can install a simple thermostat, for on/off control or offset the heating curve.
what is yr unit type?
what is yr room sensor type?
i think to set a starting dm to smaller is a good idea.
please find me on skype or write to me an e-mail.