NH3 pump or DX

[Samarjit Sen]

I would like to know for a small unit of say 60 kw for maintaining a Room Temperature of - 32 oC, with Ammonia as a refrigerant, is it advisable to have a pump system or a DX system.

Thanks.

[US Iceman]

Samarjit,

You need to see if the TXV and evaporator manufacturers will provide equipment suitable for this cold of a temperature using DX on ammonia.

DX control with ammonia at low temperatures can be a big problem.

The simplest way to do this if you only have one or two evaporators is to use flooded coils on ammonia. If you have many evaporators then a liquid overfeed system (pumped) can be more cost effective than flooded.

I do not like DX on ammonia for anything, but that is just my opinion.

[Samarjit Sen]

It is just one room meant to harden the ice cream. The total heat load comes to about 56 kw. On the bsais of this I selected the compressor. Now as far as I know that with ammonia it is not possible to attain this temperature without an additional booster compressor. That means the cost goes up as well the system becomes more complicated. I am thinking of using 4 compressors each of 14 kw at - 38 oC Te and 20 oC Cond. For the condensing temperature I propose to use chilled water at 7 oC inlet through the Shell & Tube Condenser. For this I will definately have to use an additional smaller capacity compressor. The Compressor I propose to use is open type Bock.

Please could you guide me if I am wrong. You know Mike I am not much aquainted with ammonia.

The evaporator manufacturer has offered both the DX and the Pump system. I very well remember that some where in the forum, Mike had earlier discouraged me or some one from using DX for NH3.

[nh3wizard]

I don't like DX either, and was just looking at it cost wise, what kind of problems have you experienced with DX at that temp?

[Samarjit Sen]

I guess using a DX system would not be proper. So it has to be a pump system. Either I shall have two compressors installed or 4 each with its individual Evaporators. But considering the cost, I feel that I shall prefer to install two nos of compressors and each connected to two coils. Before I seek further opinion I would like to know if my thoughts are correct or not. For two units I shall go in for Vilter as the same is being manufactured in India with Frick.

[US Iceman]

Samarjit,

You also have to think about defrosts too. If you have 4 evaporators, one of the four should only be in defrost at a single time. Then the other 3 coils would be cooling the room and providing heat for the hot gas defrost cycle.

For a load of ~60 kW you may be able to use only three compressors. One low-stage compressor, 1 hi-stage compressor, and 1 for a spare compressor (piped in to allow changing for either of the compressors).

[Samarjit Sen]

Could I have a single line drawing of the system with the equipments .

[Samarjit Sen]

Does Vilter have a compound reciprocating compressor suitable for Ammonia.

[NH3LVR]

Does Vilter have a compound reciprocating compressor suitable for Ammonia.

Yes they do. Pipe to an Intercooler and you are done. Very good machines.

[ntfreezer]

Why not use a frone DX system, it is very simple.
R404A is a good refrigerant.

[Samarjit Sen]

Yes ***** wuld be much better. We have been so far using ***** 22 refrigerant for our projects for - 35 oC and even for Rm Temo. at - 40 oC. In the same site we have installed three units with 22. The client now wants with Ammonia.

As we have not done much with NH3, I am seeking the assistance of you members to guide me.