hot gas defrost for large ref. units - monoblock

[smpsmp45]

We had installed 5nos 60 HP units for a large cold store. The defrost is with elec heaters at present. Now the system is almost 10 years old. When te heaters in the coil get damaged, the replacement is a big issue. So we are planning to change over to Hot gas defrost system I had seen a carrier article on precautions on such large units.

But I want to get the practical aspects on this. What I had seen that the Liquid from evaporator during HGD is transferred to Receiver & does not go to the compressor. But then how compressor runs as it ahs to get gas somehow?

[GXMPLX]

Don't do it.

If the evaporator is not designed for gas defrost you will get leaks very soon more if it is old or has corrosion.

The suction accumulator is undersized and you would need to change it.

Try placing electric defrot in the front of the evap and below the coil with metal clips. With this you should easily remove them.

If you have frost problems you should recalculate your evaporator surface, placement or defrost control. This also means to think where does the water come from and defrost thermostat bulb placement.

[US Iceman]

I can't imagine a more difficult project than trying to convert a lot of electric defrost evaporators to hot gas! The amount of retro-fitting that would have to occur would be very high.

I don't think it's impossible, however, the evaporator modification required would be the most difficult.

And, as you say you have to have a gas source for the compressor to provide hot gas.

A company called Kramer-Trenton many years ago had a system like this that used hot gas defrost on a single compressor/evaporator system. Their patent covered a concept that used a small tank that evaporated the returning defrost condensate from the evaporator to create the suction gas for the compressor. You might still be able to find some links for this on the web.

They were complicated little systems that did work, but not much fun to service...

[smpsmp45]

That is what I was thinking. Since no one is doing that, there must be some reasons As explained by USiceman.

[GXMPLX]

That is what I was thinking. Since no one is doing that, there must be some reasons As explained by USiceman.

In a one evaporator one compressor system it is not even clear if you would save energy doing hot gas defrost.

You can save if you can defrost some evaps while using the compressor on others to cool.

In this case I don't think it is worth the trouble either.

[US Iceman]

Depending on the system configuration hot gas could(notice I said could) be an alternative. If the existing systems are a single evaporator/compressor it would definitely be the worse case scenario.

An alternative solution might be to group the compressors into something like a rack system (common system) so that using hot gas defrost could be done.

The easiest way I can think to convert the coils to DX is to change the distributors and use a side port distributor for the hot gas. Dump the hot gas into the distributor tubes and voila, instant hot gas defrost. You still have some modifications required for valve, etc but these are discussed in the hot gas paper smpsmp45 found the other day.