Increasing Condenser/Unit Capacity Advice

[CoolerLuke]

I would like some advice on how going about fixing a problem for a Restaurant customer I do HVAC repairs for.

Back in 2007 I installed a "Drink Slush Machine" (Think Margaritas) with a remote condensing unit. It works fine, except in the summer months, it isn't freezing the product as fast in the summer as in the winter. It hasn't been a problem until now. But now, he has built the business up and now is having problems in the summertime keeping up with the demand. He says he doesn't need a bigger machine, only that he needs this machine to preform like it does in the winter months. It isn't that he is making more slush in the summer time. In fact he told me he sales more during the winter. That has me scratching my head. LOL Anyways

So I am thinking the evaporator is not the problem, it just needs a bigger condenser, or condenser Unit.

I do mostly repairs, I am not much of an engineer. But a few ideas I have.

1. Bigger Condenser Unit Option: Install a bigger generic unit. (This is not cost efficient, it would be definitely too big for winter operations. And cost of replacement of a perfectly good unit. Just manufacturer undersized. RRRRR)
2. Booster Option: Buy a smaller generic condenser unit and install in tandem with the unit that is installed. And have a temperature or pressure switch on the liquid line to turn on the "Booster System" during the months the original condenser unit is lagging so both are running during Summer months and only the original unit is running during the winter months. (Would I have problems hooking two different rated units to the same refrigeration circuit?)
3. Increase Unit Performance: Some how increase the heat rejection rate of the condenser during hot summer days.

Thoughts or suggestions would be greatly appreciated.

Parameters:
Outside Ambient Temper range: -20F to 110F
Product Temperature: 18F to 22F
Condenser Unit BTU Rating: 16,000 BTUs

Thanks
-CoolerLuke

[joe-ice]

Would spraying the condenser with cool mains water be an option.Have done this in the past on old condensers past their sell by dates to keep plants going during hotter days

[CoolerLuke]

Would spraying the condenser with cool mains water be an option.Have done this in the past on old condensers past their sell by dates to keep plants going during hotter days

Not an option. The condensing unit is air cooled. Sorry for not mentioning that.

But, thanks for the suggestion.

We did figure a way to have the incoming product to be 35F, before it goes into the machine, which helps, but, not enough.

-CoolerLuke

[flyinkiwi]

Bigger unit sounds like a good option, but fit it with an EPR and Head pressure control so as to maintain correct temps/pressures.

It's too small to be worth considering a digital scroll or multiple compressor system, and the cost of those two options would be prohibitive.

What is your cold water supply temp?
Would connecting a water cooled desuperheater be an option?
Perhaps a water cooled sub-cooler?
Two possible ways to increase unit capacity without replacement.

[flyinkiwi]

Not an option. The condensing unit is air cooled. Sorry for not mentioning that.

But, thanks for the suggestion.



We did figure a way to have the incoming product to be 35F, before it goes into the machine, which helps, but, not enough.

-CoolerLuke

I think Joe means trickling water over the face of the condenser coil, in effect giving you an evaporative condenser.
I've had to do the same thing a few times in the last week with the run of weather we've had here. Works a treat, costs peanuts, stuffs the coil completely!

[joe-ice]

I think Joe means trickling water over the face of the condenser coil, in effect giving you an evaporative condenser.
I've had to do the same thing a few times in the last week with the run of weather we've had here. Works a treat, costs peanuts, stuffs the coil completely!

Correct ,wouldnt be hard to set it up permanent with a cheap thermostat and water solenoid

[install monkey]

move condenser inside to a stable ambient and duct rejected heat outside

[Magoo]

Increase liquid line sub cooling by fitting a suction/liquidHX before evap, and extend liquid line as multil loops across air on face of condenser, increase blade pitch on condenser fan to move more air. extra sub cooling increases evap effective capacity, reduces flash gas at evap. On average every two degrees C extra sub cooling will increase evap capacity 1 %. dependent on sugar content you could pre cool product to 0'C , or even lower.

[CoolerLuke]

Oh I see now about the water trick, by trickling water over the condenser coils. (Slaps forehead)
Can't, area is prohibitive. Neat trick though. I'll put that in my bag of tricks for future problem childs.

Sub-Cooling might be an option or extend liquid lines in the air flow, I'll have to stop in and take a look for possible structural limitations.

If not, sounds like installing a bigger unit with an EPR and Head pressure control .

One question though, flyinkiwi, you say a 2 condenser system would be cost prohibitive.

I am a bit confused, can you help correct my logic: If I use the small condensing unit this is installed now, and add a second small unit(The booster Unit), how would that be more expensive than installing one BIGGER unit? I am also thinking it might be a good fail safe down the road if one unit fails he can still operate on one until a repair can be made.

Thanks for your time, thoughts, and suggestions guys. Much appreciated.

-CoolerLuke

[flyinkiwi]

Oh I see now about the water trick, by trickling water over the condenser coils. (Slaps forehead)
Can't, area is prohibitive. Neat trick though. I'll put that in my bag of tricks for future problem childs.

Sub-Cooling might be an option or extend liquid lines in the air flow, I'll have to stop in and take a look for possible structural limitations.

If not, sounds like installing a bigger unit with an EPR and Head pressure control .

One question though, flyinkiwi, you say a 2 condenser system would be cost prohibitive.

I am a bit confused, can you help correct my logic: If I use the small condensing unit this is installed now, and add a second small unit(The booster Unit), how would that be more expensive than installing one BIGGER unit? I am also thinking it might be a good fail safe down the road if one unit fails he can still operate on one until a repair can be made.

Thanks for your time, thoughts, and suggestions guys. Much appreciated.

-CoolerLuke

If you connect two condensing units to a common suction, you will have difficulty keeping the oil level in the two compressors balanced unless you have an oil balance line between the two at the level of the oil. Especially with two completely different condensing circuits, it would be a nightmare.

If you can achieve it by having a second complete system (condensing unit and evaporator), by all means, knock yourself out.

I think the amount you would spend effecting a balanced oil system for two completely different condensing units on a common evaporator would be far in excess of the cost of a bigger unit plus controls in the first instance.

Your most economical solution may be to increase your condenser capacity, either by using a larger coil, increasing airflow as Magoo said, or using other means to remove heat (Desuperheater, external subcooler).

Edit: Yes, it would ultimately be more expensive to use 2 smaller units rather than one larger one. While it will be cheaper to add a smaller one to increase installed capacity, that may not be practical for the above reasons.

[Tesla]

Hi Cooler luke
Your best option is to follow Magoo's advice to the letter - not heat exchanger or extend liquid line cooling but both and the other too. This should get you and customer out of trouble in the summer until demand increases even more. The other option is to buy a larger capacity machine - there should be no problems at reduced loads.

[Brian_UK]

Can you install a second condenser fan coil unit to increase your sub-cooling?

Have you got a spare coil from an old unit somewhere perhaps??

[CoolerLuke]

Thanks FlyinKiwi for the explanation. The straight and narrow is now a little more straight . :P

Looking at Telsa's advice to follow Magoo's advice. I will be stopping by tomorrow to take a look at the unit to see if the modifications can be made. And let the owner know his options.

Brian, I was searching the web for just a condensing coil, but, now that you reminded me I may have one in my junk pile. I don't know why I didn't think of that.(Slaps forehead again) I must be getting old. LOL

I always keep old parts for just this type of situation.

Thanks again for all the input. Very much appreciated.

-CoolerLuke

[RANGER1]

CoolerLuke,
I think you need more detail of the current setup in summer.

It would be ideal if you can give us

refrigerant type
pressures & temperatures
super heat of evaporator
subcooling of liquid line, if it has any.
length of liquid line & how it is run
sight glass observation if it has one, to know if full or has gas bubbles.


For all we know liquid line is full of flash gas in smmer!