low humidity cold rooms

[nambiandy]

Hi

Is it possible to achive 30% Humidity in 4degC cold room with evapaorator or dehumidifier is a must , if so how do we calculate how much CFM is to passed through dehumidifer?

Asuming room size10 x 8 x 8 ft(ht) , heat load calculated 1.5Tr at operating condition

anand

[Andy]

Hi Nambiandy

yes it is possible, with or without a dehum you could blast freeze the air then heat it up again to the required temp and humidity

Kind Regards Andy

[Pooh]

What product are you storing in the room and how often will the air be changed. As Andy said you should be able to do this without a dehumidifier if the delta T across the coil is kept as low as possible so you do not freeze it.

Ian

[Samarjit Sen]

Low humidity in a room of 4 Deg C can easily be achieved without any dehumidifier. You have stated the size of the room, but not the product or the use of the room.

Low humidity shall be achieved either by the way Andy has suggested or by selecting the proper coil and maintaining the required Td.

If you desire you may send a PM to me and may be I shall be able to help.

[Peter_1]

Samarjit,
why not share your knowledge with everybody?

[Darshi]

I think refrgeration dehumidification at these conditions is not energy efficient .After the product reaches equilbrium the moisture load will be mostly the infilteration load .after the steady state is achieved there will be no product load .
Because ,it is a small cabinet ,it should be a steel or aluminium sandwitch panels.At best it looks to me a 50-100 cfm desiccant dehumidifiers should do .
You have two good vendors in India . Bry air and Appidi .Good luck

[Samarjit Sen]

We had done a couple of jobs of low humidity for a Research Institute in the Northern part of our country. The temperature required was 4 to 8 Deg. C with a RH of 30 to 50 %. The requirement was to adjust the temperature and RH as per requirement.

To meet this we had provided two row coils with a big face area and a fin spacing of 12 fpi. The Td was maintained high and we had provided a Evaporator Pressure Regulator in the system. The chambers were not very big.

As the work was executed a long time back, I am unable to recollect the details of the controls provided. However the plant did maintained the required conditions.

With best wishes,

[Darshi]

In India ,Before 80s all the pharma low humidity jobs used refrigeration dehumidification with electrical reheat .No doubt humidity even 10 % was maintained but of course at a colossal energy cost.
Refrigeration engineers designing commercial /industrial refrigeration and Air-conditioning have not been very energy sensitive.
With the power costs going thru the roof we should look at the operating costs of the installation as the key issue.
The point I was trying to make was the life cycle costs of the installation.

[Darshi]

Hi Nambiandy

yes it is possible, with or without a dehum you could blast freeze the air then heat it up again to the required temp and humidity

Kind Regards Andy

andy , that costs a fortune in energy costs

[Samarjit Sen]

Dear Mr. Darshi,

You are very much correct in your assessment. In our country, no one is trying to design an energy efficient and saving refrigeration plant. The users see the capital cost. It is only when they operate the plant, they find the running cost is high and subsequently due to large energy bills, the plant closes.

I blame the refrigeration firms and the engineers. They should educate the clients and explain the situation, instead in their eagerness to get the job at a low price they offer low cost plant with high power consumption.

In my small way I am trying to bring some changes and may be a very small population shall listen. But then it is a start and I hope the next generation or the young engineers of today will carry on from there.

With best wishes,

[US Iceman]

With the power costs going thru the roof we should look at the operating costs of the installation as the key issue.
The point I was trying to make was the life cycle costs of the installation.

This is very good advice. All of us should be using some tenet of the "value engineering" process for making decisions on how a system should be designed, installed, and operated.

As Samarjit Sen stated, the first cost tends to drive the system design since the owners are only looking at "money out of pocket", which does not include annual operating costs.

This is a vicious cycle to break.

[Samarjit Sen]

I do not know how it is possibe, but I am sure that some one may suggest as to how to standardise the business ethics in our field so that the dirty competition which we all face in some way is elliminated. We are proud of being a member of this forum and be associated with so many nice and helpful engineers and I am sure that this forum is the right place to create an atmosphere of better engineering practices.

[nambiandy]

Thank you all

The requirement is for Pharma plant and the door opening would be 3 to 4 time in a day.

I totally agree that we should go for cost effective operational solution .

As i understand from the members that going with dececant type dihumidifer would be an appropriate solution

thanks

Anand

[Kevin Yeo]

Dear Samarjit Sen,

May I ask you what is the function of evaporator pressure regulator of reducing room %RH? Is it because you have selected high TD1 in your evaporator and you need the pressure regulator to regulate the pressure in accordance to compressor suction pressure?
I am handling a small pharmaceutical project too. The temperature requirement is the same but there's no requirement on humidity control. May I ask is this a concern if the products are packed?
Thanks a lot

Kevin

[Darshi]

Kevin,
Humidity is relevant for product packaging in pharma industry .
Some effeversant products may require 30% or lower humidity .All gelatine capsule processing and packing area require Rh to be maintained at 45% or lower.
For general packaging and human comfort the space must be at 50- 55 % relative humidity.

[Gary]

In order to achieve 30% humidity @ 4C, the coil leaving air temp needs to be below -11C. Then it is a matter of running the system long enough to do the job. That's where reheat comes in.

Reheat does not remove moisture from the air, it simply extends the run time.

Downsizing the system also extends the run time and is far more economical.

[Sanjaykale1]

Dear sir
I have to build a cold room Temp. 8 Deg. C. and 40 RH for seed storage ,i am thinking to use auto defrost dehumidifier in side the room.
will this work?
Regards
Sanjay Kale

Low humidity in a room of 4 Deg C can easily be achieved without any dehumidifier. You have stated the size of the room, but not the product or the use of the room.

Low humidity shall be achieved either by the way Andy has suggested or by selecting the proper coil and maintaining the required Td.

If you desire you may send a PM to me and may be I shall be able to help.

[Peter_1]

Sanjay Kale,

Our great appreciated member Mr Samarjit Sen passed away some time ago.