defrost on freezer coldroom

[andyh]

I have a freezer coldroom with two seperate systems.
A control panel for each system. One system has a conventional defrost timer with built in fan delay and an eliwell controller (stat only) ie 1 relay. There is an evap
termination stat as well.

The other system has an eliwell 974 controller - 3 relays fan def comp.

The problem is they defrost at different times. so one maybe cooling while the other is defrosting.

What would be the best way to adapt them to defrost together.

Many thanks andy

[Brian_UK]

Sounds as though you want to control both systems with just one controller.

Can you take control signals from the 974 control system and connect them to the other control panel?

[chilly]

Agree with brian..

Or change the controler so they match.

[andyh]

Yeah! this can easily be done and have thought of doing it.
The only thing is that if the system with the coil probe attached has a gas leak or any other outdoor unit problem the other system wont start too due to coil temp.
The customer would have to accept that it would now be one complete sytem and defrosting efficiently.

Cheers!!

[Peter_1]

There's a Digital input on the models with an LX behind the type (cost almost nothing more then the conventionale version, and therefore, we only use LX models) which you can activate via parameter H21 till H32 as a defrost cycle.
This input from controller 2 comes from controller 1.

Carel has a range with the same possibilities.

[bernard]

Hi

Surely the whole point of having two seperate systems is for them to back each other up, working independently and defrosting at alternate times so as there is not a massive temp drop.

Regards Bernard

[Peter_1]

.. working independently and defrosting at alternate times so as there is not a massive temp drop.

When you defrost 2 evaporators in a freezer at different times, then much of the heat generated in the defrosted one will be lost in the roo mdue to air movement of the running one, unless you can shut it off mechancially while defrosting.

[old gas bottle]

theres two ways of looking at this as bernard and peter says, why do you want to alter it?,is there a problem with the defrost?,if the coolers are not to close to each other i would leave it as is so the systems are independant,if they can influence each other peter has bought up a very important point,as a rough guide,the coolers need to be approx 3mtr apart mounted on the same cieling,facing the same way to be independant, otherwise i would adapt or build a new panel with inerlocks on the contactors,fully protect all the major components with MCB,s then you will still have a good level of back up.dont forget to set the elliwell so in the event of a probe failure it still runs.

[andyh]

the coldroom is approx 4m x 4m and both evapourators almost face each other but are slightly offset so if you can imagine they are in opposite corners and recirculating one anothers air.

I think it was originally designed as a blast freezer but the customer no longer needs this application as everything goes in at -18 or below.

The room will achieve -21 on one system but the customer likes both systems operating and this is when the problem starts as ice slowly starts to accumulate around both coils and ecspecially the driptrays.

This is due to the fact that one will be trying to defrost whilst the other is in cooling mode and temperatures are well below sub zero.

I'll take a look at the LX and carel range and decide what to do like you suggest Bernard I will certainally
modify it to keep both systems in operation indepandant of each other except for defrost in case one does fail.

Thanks for your input guys
andy

[frank]

If one system is capable of holding the load then they should be used as run/standby (duty sharing) - not both at the same time.

[Peter_1]

If one system is capable of holding the load then they should be used as run/standby (duty sharing) - not both at the same time.

Well, or as we set the thermostats.

Thermostat 1 at -20°C and 2°C DT is starting at -18°C and stopping at -20°C.

The 2nd at -17°C and a DT of 3°C or -16°C and a DT of 4°C so that it's ready as a back up and pulls the freezer to the same initial temperature of -20°C, eventually togetehr with n°1.

2 will also start then when room for some reason comes too warm (for example introducing fresh goods)

[Bones]

if your looking at controlers i have found the carel IR33 range really good for freezer room aplications especially the one with real time clock built in, (cant think of the model # atm).

IR33COHBOO - is the controlers i have been using.