daikin return air problem

[Kev The Tool]

Hi Guys,
Got called to a daikin twin split today, indoors are two 125 ducted units sitting on a mez floor above an office inside a warehouse, customer complained that when the units are heating they don't cut out when they reach set point. he said it had been like this for 5 YEARS !!!, he also said two different companies had been out but could offer no explanation. after i lifted a couple of tiles around the return air grilles i believe i found out why it wasn't cutting out at set point. return air grilles turned out to be just grilles with no return air getting back to the evap, evap is situated in a warehouse where the ambient was 12 degrees c, i just cannot believe two " Engineers " did not spot this. am i missing something ?

[Brian_UK]

am i missing something ?Nope, there are some dumb people out there.

Can you reset the controller to accept the room sensor instead of the duct sensor?

[multisync]

I have had that several times. We were installing some splits in a similar set up. The customer complained that his old 4 14kw Fujitsu ducted units never got the space warm in winter or cool in summer.
I told him it was because he had no return ducting and was taking the air from the void. He was very skeptical so I made a cardboard box return duct by taking out 2 tiles and taping it around the return.
We then measured the air off temps and compared.

He couldn't believe the difference as the air was 15 deg colder. (this was mid summer and the roof void hit 40c) We then had metal ducts made for all 4 units and he was delighted.

Convince him that he MUST get return ducting fitted and he will save a fortune.

[frank]

And install the remote wall mounted sensor into the room at 1.6m above floor level (and out of direct sunlight and draughts)

[Bartolo]

In DAIKIN units You can switch duct sensor to remote sensor for temp. reading (field settings of indoor unit - service mode), so the units will cut out when the remote sensor will read the setpoint temp.
That schould solve the problem.

[Kev The Tool]

Hi Guys,
i spoke to the customer today and he is happy to go with remote air sensors, he has the same system downstairs and he says he is having the same problem but not as bad, had a look, again no duct attached to return air but it does have a VAM unit supplying fresh air but has no heater battery or fan speed controler. he is happy for me to quote fitting these for him, but as i am not overly familiar with these VAM units i wondered if anyone could throw any light on the situation, as regards to whether they have an internal heater, and control options. thanks in advance guys.
Kev

[VRVIII]

Hi Guys,
i spoke to the customer today and he is happy to go with remote air sensors, he has the same system downstairs and he says he is having the same problem but not as bad, had a look, again no duct attached to return air but it does have a VAM unit supplying fresh air but has no heater battery or fan speed controler. he is happy for me to quote fitting these for him, but as i am not overly familiar with these VAM units i wondered if anyone could throw any light on the situation, as regards to whether they have an internal heater, and control options. thanks in advance guys.
Kev
Hi Kev,

VAM units have 3 speed fan motors and they are not designed to be used with a fan speed control device.
A duct electric heating element is normally used to prevent frost damage of the VAM heat exchanger and usually controlled via a small thyristor pack with a set point of about 5 C.



Precautions when using a heater element:

There is a min distance required between heater & VAM unit (I think this about 1.5~2m)
An air flow switch must be installed to switch off heater if no air flow is detected.
Heater element must incorporate a manual reset overheat protection device
The VAM unit fan motors must be set to start 10secs before heater is energised and must continue to run for 3min after heater has been de-energized.

[Kev The Tool]

Thanks for the info i will relay to customer and see what he wants to do. thanks again
Kev