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Gaz E
14-01-2010, 06:25 PM
Hi all
is any one having problems with Daikin R407c heat pumps not heating correctly when outside temp drops below freezing,the discharge pressure gets to only about 210psig,air off temp at indoor unit is only 32-33deg ,out door coil frosts up & defrost is working ok(approx every half hour) & all 4 units have correct charge in.
Is this is a common problem with R407c?
am gettin grief from customer so any feedback would be gratefull.

VRVIII
14-01-2010, 06:59 PM
Hi all
is any one having problems with Daikin R407c heat pumps not heating correctly when outside temp drops below freezing,the discharge pressure gets to only about 210psig,air off temp at indoor unit is only 32-33deg ,out door coil frosts up & defrost is working ok(approx every half hour) & all 4 units have correct charge in.
Is this is a common problem with R407c?
am gettin grief from customer so any feedback would be gratefull.

Hi,

Your problem sounds more like a design issue, if you have a look at this previous thread http://www.refrigeration-engineer.com/forums/showthread.php?t=22728 you will find a detailed post by Thermatech that explains the most common VRF/VRV design/install issues.

redroge
14-01-2010, 08:16 PM
its not just daikin leave them on 24/7 to try to get the rooms up to temp. having the units off overnight they take ages to heat the rooms from cold.

DEVIL
14-01-2010, 08:26 PM
Way the conclusion that it is a VRV ??

Gaz, give us some more info , what type of indoor what type of outdoor installation time , in/out temperature, running hours until the problem and so on

Gaz E
16-01-2010, 11:14 AM
sorry guys,should have said,they're all single splits,but went back to site y'day to find all 4 running ok,outside temp was 3deg,air off at indoors now 42deg & warming rooms nicely,will take redroge's advice tho & try leaving units on 24hrs,at moment they're only on between 8am-5pm so we'll see if that make difference especially when temp drops below freezing again.

back2space
22-01-2010, 02:21 AM
sorry guys,should have said,they're all single splits,but went back to site y'day to find all 4 running ok,outside temp was 3deg,air off at indoors now 42deg & warming rooms nicely,will take redroge's advice tho & try leaving units on 24hrs,at moment they're only on between 8am-5pm so we'll see if that make difference especially when temp drops below freezing again.

I wonder what the problem was then, my unit sometimes does that if its at freezing outside, air off about 31C next day it will be ok...

THere supposed to work down to -15C though!!!! So dread to think what air off would be at that!

desA
22-01-2010, 06:04 AM
Air-source heat pump evaporators are very sensitive to air conditions onto the coil. Temperature & RH% changes can have a huge effect on performance - day-to-day. If conditions are in the freezing range, or in/out of it, the coil performance will suffer.

Obviously the method of clearing the coil during defrost will also be important.

As the outside temps drop, so does the heat lost from the heated space. This then demands more heat from the heat-pump, at the very time it is struggling to extract the energy from the atmosphere.

To be honest about these type of applications, installing an air-source heat-pump in such conditions is inappropriate use of the technology. If the heat-pump is installed inside, or in a roof space, with cold air ducted outside of the space, then this would perhaps alleviate a lot of these difficulties.

multisync
22-01-2010, 10:57 AM
We had loads of VRV's giving trouble during the cold spell. Now that's gone they are -mostly- all back working ok..

back2space
22-01-2010, 02:11 PM
If the heat-pump is installed inside, or in a roof space, with cold air ducted outside of the space, then this would perhaps alleviate a lot of these difficulties.#

AIr has still got to make up the air that been ducted outside from the unit so where is this air coming from? You cant say from the living space as this air will be warmer but then where does the air come in from to make up the air that has been sucked into the loft? It would eventually come in from outside and this would mean a cold living space so there is no way round it, the only way to have the heat pump installed is outside or if inside you need both inlet and outlet ducted to the outside.

Otherwise the unit will turn the loft into a giant fridge freezer. ON another forum a user had installed the condenser in the loft and it had frozen everything with about an inch of ice and this defrosted and flooded the roof and ceiling area below.

desA
22-01-2010, 02:57 PM
Good points.

You'd have to think carefully about your insulation between loft & house, plus air flow strategy within the loft. The cold air has to exit, of that there is not question.

I'm not from your part of the world, but there will be a way, I'm sure.


Otherwise the unit will turn the loft into a giant fridge freezer. ON another forum a user had installed the condenser in the loft and it had frozen everything with about an inch of ice and this defrosted and flooded the roof and ceiling area below.

Now, that must have been fun... :D