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Friobernal
12-08-2005, 10:47 AM
Hi;

Have anybody installed an evaporative condenser in an ammonia system for a reverse cycle?

Where would you feed the evaporative condenser working in mode evaporator, i mean top feed or bottom feed?

What problems have you had?

Beste regards

US Iceman
12-08-2005, 02:05 PM
Hi Friobernal,

This is a new application for me if this is reverse cycle. Are you trying to make a heat pump? Or, are you wanting to use the condenser coil only for cooling?

The use of the condenser coil for cooling only is similar to hydrocooling for vegetables or fruit. This is sometimes used in the field to cool the vegetables or fruit after they are picked. But before they are shipped to the processing facility.

Can you provide more detail?

I want to add that a similar type of coil design is also used in thermal storage. If you not familiar with this it is sometimes called an ice bank. The coil is placed in a tank of water. Water freezes around the tubes, usually at night. During the day, the cold water is pumped for process cooling.


Thanks,
US Iceman

Friobernal
13-08-2005, 11:05 AM
Hi Iceman;

This is already done in the company iīm working for right now, but it has to be perfectioned.

In oranges processes, we need a fast cooling as in most vegetables, we do this in a pre-cooling tunnel, something similar to;

http://www.pretecval.com/

Then we can store oranges at Tc = 3/4šC, but sometimes is neccesary adding heat to acelerate rippening process.

This has usually been done with electrical heaters, like a long defrost.
And the idea is heating with hot gas, but we need one of the Evap. condenser working as a condenser and the other one as evaporator to mantain the circuit (we need surface).

This has been already done with a PHE condenser (of course it is much more simple). but with an ECond it is much more tricky (we havenīt got constant conditions; summer/winter...)

P.D. Iceman, till one year ago i worked for a known PHE manufacturer, if you want some info let me know

US Iceman
13-08-2005, 11:57 PM
Hi Friobernal,

The system you are describing seems like a heat pump. Cooling the oranges and rejecting heat with the condenser. When the oranges need to be ripened, heat from the refrigeration system is added to the orange storage room.

It would be helpful if you could send me a flow diagram of the basic system if you can.:confused:

When the coils are used as an evaporator are they cooling water, or is the coil being used as an icebank?

This application sounds fascinating. I would be interested in learning more.

Thank you,

US Iceman

Friobernal
16-08-2005, 08:53 AM
Hi Iceman;

The coil of the evaporative condenser used as an evaporator doesnīt cool water, just air of the ambient. Because sometimes we donīt have oranges to cool in the process to produce heat enough for rippening process. Thatīs why additional heat exchanger surface is needed

They are standard evaporative condensers Baltimore

Regards

US Iceman
16-08-2005, 06:52 PM
Hi Friobernal,

I think I understand your process now. Let me know if this is correct.

The extra condenser coil will be used as an air cooled evaporator for cooling ambient air. The heat absorbed from this coil will be used to provide heating (from the refrigeration system) for the oranges during times when there is no cooling load.

Do I understand your process properly?:confused:

When oranges are being cooled do you want to use the new coil for condensing to help reduce the condensing pressure also?

If all of this is correct, then we have to assume the new coil could be used as an evaporator or evaporative condenser. If this is the case, I now have an understanding of your original question. I have done something similar to this a long time ago.

Since the condenser coil is designed for gravity drainage; gas IN (on the top connection) and liquid OUT (on the bottom connection), it is a simple assumption to say the process works in reverse as an evaporator; Liquid In (on the bottom connection) and gas OUT (on the top connection). The top connection would have a liquid and vapor mixture leaving the coil.

It is a simple gravity flooded evaporator in this mode of operation. This would look like a flooded ice bank coil. Gravity flooding of a big coil will of course require a larger refrigerant charge and a liquid separator.

To convert this from a gravity flooded coil (for cooling) to a coil used for condensing (for heat rejection) we need to have some automatic control valves to switch the flow of refrigerant as required for the operation.

This should be fairly simple to do, but hard to describe in a short explanation.

One problem I see is during the time of changing the mode of operation (evaporator to condenser). During cooling, the coil will be about 70% full of cold liquid. About 30% of the coil volume will be vapor. This liquid should be drained out or isolated during the heat rejection process. This piping could be similar to gravity flooded air-cooling coil, piped for hot gas defrost.

If the coil is allowed to switch from low-pressure operation to high-pressure operation quickly, when the coil has a lot of liquid in it, you could develop a liquid hammer situation. This could cause the coil tubes to burst. This can be a big problem.:eek:

Is this what you are looking for??

Are you using the BAC condenser coils with fins?

If I am on the right course with my understanding, let me know and we will see if we can work through this application.:D

Best Regards,
US Iceman

sterl
16-04-2009, 02:06 PM
If I read this correctly: There will be one EC condensing to maintain refrigeration; so some evaps are operating, at the same time as one EC is "switched" to be a dry air cooler. The latter will create enough false load on the plant to maintain hot gas flow for warming selected spaces to promote ripening. Implied is that the spaces being cooled at that time represent less heat being extracted than the required heat to be delivered to the ripening spaces.

We have reverse cycled evap condensers (dry) but not often...We did it on a wholly portable freezing tunnel that only operated at "crop" time ODA temperatures...We were not concerned about low ambients and the engine driving the compressor added to the heat.

At low ODA temperatures the "holding" refrigeration load and the heat transfer at the "outdoor cooler" are both going to be low: so the Heat of Rejection is going to be low; so heat available needs to balance with heat required by rooms in Ripening Mode. This becomes design target.

If the temperature rise for ripening is a short term condition and your local ambients can get low: You may be far better off to "bank" refrigeration in an ice builder when your heating load is greater than your cooling load; and harvest that when your cooling load is greater than your heating requirement. This would be a preferable design if the heating/cooling overbalance occurs for more than a couple hours, each day.

But if this misbalance is a twice a month for a matter of hours routine, and your ambients are continually higher than house sat suction temp by at least 12-deg. C. it may all make sense. As Iceman indicates: The transition from one mode to the other needs to be done pretty carefully, and there will be a considerable accompanying shift of plant charge, and a short term lack of cooling while the pressure is lowered in the coil....
Other than a flock of control valves and a sequencer to shift them: all it really needs is a righteous surge drum....Our old error involved piping it all so the Discharge Gas passes through the surge drum during refrigeration. That got pretty ugly....