View Full Version : desuperheater / economizer

12-07-2002, 06:09 PM

I would like someone explains me what are a desuperheater and an economizer, and how they work, where, why...? Iīve been reading but there isnīt much books in spanish about these things. Donīt worry to be very technical, iīve got time and a good diccionary :D

13-07-2002, 01:31 AM
I would guess that you are referring to scrolls or screws because that is where I see the term "economizer" used most often. But the terms apply to recips as well, at least in principle.

Desuperheating applies to desuperheating the discharge gas of the compressor. The economizer is most often referrred to as a device providing liquid subcooling on two-stage systems. It utilizes the second stage suction temperature to evaporate liquid in a heat exchanger in which the other fluid is the liquid feeding the refrigerating evaporators. Since the EER or COP of the high stage compressor is better than the low stage compressor, a good percentage of the net refrigeration effect is accomplished at a more energy efficient level.

On rotational compressors such as scrolls and screws, the desuperheating method is done by liquid injection at some midpoint of the compression process. It's purpose is to cool down the compressed gas to temperatures that will not scorch the oil and avoid other chemical breakdowns that can play havoc with the system.

On reciprocating compressors, liquid injection is also commonly applied. Copeland Demand Cooling with R22 on low temperature applications serves the same purpose. Other methods such as injecting liquid into the suction line are alos used.

The difference between the reciprocating desuperheating methods when compared to the rotational desuperheating methods is that the compressor capacity is diminished on the recips whereas it is mostly unaffected on the screws and scrolls.

Economisers are mechanical liquid subcooling. Mechanical liquid subcooling applies to single stage compressors as well as two-stage compressors.

Mechanical liquid subcooling is simply using a higher efficiency compressor to absorb heat from the liquid provided by a lower efficiency compressor. In a supermarket, for example, you could use a compressor unit operating at an EER of 9 to cool the liquid of a compressor unit operating at an EER of 4. You can achieve an efficiency improvement of 15% to 25% with such a setup.

This doesn't come from manuals... just stuff in my alleged brain. In other words:

Desuperheating mostly means injecting liquid into the compressor to insure the hottest that the discharge gas gets is below 300 Deg F. Normally translated to below 250 deg F where you can measure it 6 inches on the discharge line.

Economisers mostly means mechanical liquid subcooling where you refrigerate the liquid of the low temperature systems with a more efficient medium temperature suction pressure.

That's my best guess, anyway.:)

Prof Sporlan
13-07-2002, 03:17 PM
The term 'economizer' is also used with air conditioning systems that sense outside air temperature, and draw in outside air when it is cool enought to provide useful cooling.

These economizers are, of course, used on commercial equipment that run during periods where ambient temperature are cool enough to provide useful cooling.

13-07-2002, 05:21 PM
A de-superheater can also us an external source to cool discharge gasses. One example would be a plate and frame de-superheater fitted to reclaim heat on the compressor discharge line typically used to heat a weak glycol water mixture, which in turn used to heat the sub-floor under coldstore to eliminate the problem of frost heave.
Economisers are a means of stretching the refrigeration cycle, typically used with singe stage screw compressors to allow their use on low temperature coldstores or blast freezing cycles. They come in various different types, just like intercoolers.
1/ Open flash.
2/ Closed flash
3/ Direct expansion.

Various types of heat-exchangers are employed from simple coil in tank and open tank to shell and tube, shell and plate and plate heat-exchanger.

I have may have added more quetions than answers, please feel free to post again if you have any queries.
Regards. Andy.

07-05-2003, 08:32 PM
I have a desuperheater on my AC to heat my domestic water .

07-05-2003, 08:43 PM
I've seen an application whereby the discharge gas is fed through a water tank that feeds the DHW system of a commercial building. The waste heat from the compressors (4 No.) is constant as the installation is serving a commercial computer server room ( about 120kw)

When the DHW is satisfied the discharge gas is diverted straight into the remote condensers and fan speed controls take over.

The maintenance team say that vast energy savings are made by using this method.


07-05-2003, 09:12 PM
Mine has a pump. When the compressor is on the pump is on. The pump shuts off when the water in and water out temp are the same. I have a 55 gallon tank before the water heater. I cooler months it works as a preheater for the gas water heater.

It saves me about $100/year, and I don't have to worry about the cost of hot water in the summer time. I used to turn the water heater down in the summer, but don't anymore. We probably use more hot water now too.

05-08-2010, 02:58 PM
Superheat -- could you tell me the details of your setup -- flow rate of pump- type of differential temp controller ??
My 28 year old York Triton water source heat pump finally died and I am installing a 3 ton unit with desuperheat -- I have an on-demand water heater with an old water heater as a pre-heat tank to supply the heater -- I am using well water ( 54 degrees - but slightly acidic) -- heat pump is about 15-20 feet from water heater and I plan to use CPVC piping