How to reduce capacity?

[Emmett]

[quote=chrishaji;172018]Sorry Emmet, the fan is controlled by a variable frequency controller (3ph 0.75KW) and is manually operated by the grower.

I can design circuitry and software to automatically control the fan, but the problem is the need to reduce airflow on the beds sometimes, and this leads to ice-up.

I have a couple more ideas -
1. Put in an extra
duct pointing to the ceiling - this should reduce airflow across the beds, whilst still enabling max flow across the evaporator.
2. buy 2 compressors each half capacity and make it a 2 stage system. Would this be cheaper than putting a variable speed drive on the existing compressor?

Go with idea #1 it is the same concept I was attempting to convey previously, do not adjust fan speed disperse excess air to an alternative location when lower air flow is necessary. This should be relatively easy to accomplish and grower will adjust damper position rather than adjust fan speed.
Good luck with your situation Chris and please keep us informed on what solution you choose to pursue and how it works out for you.

[chrishaji]

Thanks again for your help - I've just had another idea.
What if you direct a percentage of the air from the duct inside the room (leaving the fan at 100% thus avoiding the freezeup) onto a large surface of material (or a thin tank of liquid with fins on it) that had an extremely high specific heat. The effect of this would be to buffer the cooling of the room at low loads and thereby reduce any oscillatory tendencies, whilst also reducing the airflow over the beds.
Would this work?
Chris

[The Viking]

But Chris, of course it would...

[murray75]

If there is insufficient air flow over the evaporator, it will ice up.
------------------------------------
Rather than have a control system where the compressor just comes on for cooling then stops, you could employ a cooling sol valve and a bypass sol valve. With this method you will get closer control.

[chrishaji]

Hi Murray75,
'you could employ a cooling sol valve and a bypass sol valve'
Could you explain a bit more about exactly how these two valves are fitted to the picture of my compressor and the potential cost? Can they be fitted easily to an existing system?
I've searched various sources, but I cant seem to get an exact description and apparently this method is rather inefficient.
Is it possible to exchange the compressor (copeland scroll) with a digital scroll? Would this require other expensive modifications to the pipework, evap and condenser, or is it a straight swap?
Thanks - Chris

[Yuri B.]

OP N1

it is necessary to flush out CO2 (produced by the mushrooms) to enable a good crop.
This means air changes of up to 7 per hour, i.e. around 150 x 7 = 1050m3 per hour of conditioned air from outside..

By the way, from my school days I remember that plants just need CO2 - and light - for photosynthesis (growing).

[Gary]

If the air has been cooled to 21C, then its heated by 1C you will end up with air at approx 90%RH at 22C.

Apparently you are familiar with psychrometric charts:

http://www.uigi.com/UIGI_SI.PDF

Let's imagine that the outdoor temp drops to 15C @ 60%RH. You warm that air to 22C. You now have air that is 22C @ 39%RH.

What are you going to do about it?

[VRVIII]

Apparently you are familiar with psychrometric charts:

http://www.uigi.com/UIGI_SI.PDF

Let's imagine that the outdoor temp drops to 15C @ 60%RH. You warm that air to 22C. You now have air that is 22C @ 39%RH.

What are you going to do about it?

Interesting long thread, but I have one question Gary, Have you always been as tolerant? Or does this continue to improve with age and experience

[Gary]

Interesting long thread, but I have one question Gary, Have you always been as tolerant? Or does this continue to improve with age and experience

Actually, I've become less tolerant over the years... lol

[murray75]

RE COOLING SOL AND BYBASS SOL

The cooling sol would be fitted in the liquid line just before the sight glass and and TEV. You could use a controller which would call for cooling and energise the cooling solenoid, then when the desired temperature is reached the cooling solenoid would de-energise and the bypass would come on. The bypass is fitted into the hot gas line and has a manual shutoff valve immediately before it (the manual valve is used to regulate the amount of bypass pressure-it would normally be set to 5 psi) it is then piped directly into the suction line. When the bypass is on it just keeps the compressor ticking over by stopping it pumping down and shutting off and then when a little bit more cooling is needed, bypass goes off and cooling comes on. This way you get much closer control. Unfortunately I cannot give you any costs!!

[flyinkiwi]

So many problems - so little time - so many more solutions!

But there is one option that will solve all your problems...

Hire a Fridgie!

I know this might be a bit of repetition, but every uninformed decision leads to another problem, with its own solution and problem that it creates.

Hire the guy with the knowledge to identify the root cause and fix it.