Desuperheaters

[Ålen]

Hi there,
is there anyone who can explain the differens between open/closed and DX desuperheaters? Could any of these be used for hot water preparation in a domestic heatpump using 407C or 134a?

[nike123]

Please, clarify these terms. DX usually mean direct expansion and desuperheater has noting to do with expansion.
Where did you came on these terms!

[Ålen]

Sorry, when I wrote desuperheater I ment subcooler.
Open flash subcooler
Closed flash subcooler
Direct expansion subcooler.

[Peter_1]

Are you asking this because you're using Coolpack?

[Ålen]

No, I'm not. In fact I'm looking for a way to improve the preformance of a heatpump. One way could perharps be to use a subcooler. By this I could improve the COP by subcooling the liquid before entering the expansion valve and additionally pre-heat hot water. Right? I was also thinking of the possabillity to use a desuperheater to top up the hotwater. However, I have never used these componenets and was lookning for some facts on the net an found this forum so why not putting the question here? Is there someone who could guide me in this matter?

[nike123]

No, I'm not. In fact I'm looking for a way to improve the preformance of a heatpump. One way could perharps be to use a subcooler. By this I could improve the COP by subcooling the liquid before entering the expansion valve and additionally pre-heat hot water. Right? I was also thinking of the possabillity to use a desuperheater to top up the hotwater. However, I have never used these componenets and was lookning for some facts on the net an found this forum so why not putting the question here? Is there someone who could guide me in this matter?

You could install in series with condenser (before condenser) plate heat exchanger of 20% capacity of condenser, and there it is, your desuperheater for domestic hot water of up to 75°C.

On water side of desuperheater install 3 way valve. To to prevent unbalances from occurring in the cooling circuit in the event of start-ups with very low water temperatures at the recuperator inlet, the recovery system water circuit should be configured as shown in the figure:



A low recuperator inlet water temperature would cause low condensation
temperatures and thus an insufficient pressure differential on the expansion
valve with the consequent risk of tripping the safety devices.
The sensor of the 3-way mixing valve shoul be situated at the recuperator
inlet and mixing the hot water produced with colder water from the inertial
storage reservoir makes it possible to bring the system to optimal operating
conditions in a few instants. Given that the demand for heat and the
availability of heat do not coincide, since the latter is dependent on the
compressors running, it is essential to install an inertial storage reservoir.

Also, if you don't have condensation control, you should install one.

I would not tuch suction side (subcooler).

[Peter_1]

We use a HP switch which controls the pump.
In our case, the pump must not run always.
Can't you subcool your liquid with a ground coil?
What's your actual liquid temperature before entering the expansion valve?
I suppose you will use the desuperheater only when using your heatpump in cooling mode.

[Ålen]

Thanks a lot Nike 123, this was exactly what I was looking for. However someone mentioned there can be problems with "scaling" i.e formation of limestone and/or gypsum on the heat transfering surfaces in the plate heat exhanger when producing hot water above 65 degree of Celsius. Perharps you should use some other kind of exhanger?

Peter_1, I was thinking of subcooling in two different ways; for groundsource HP with incoming brine. This will give dual effect. Subcooling liquid and pre heating brine = gain of COP.
For air/water HP it's not suitable to subcool with incoming "brine" = air, because the poor conditions of preheating incoming air. Instead I was thinking of using suctiongas heat exchanger (suctiongas/condensate). However using R 407C it will give problems with high dischargetemperatures when superheating the suctiongas. Is there any other way of subcooling the liquid in a sufficient way for a air/water HP?
And no, the desuperheater will be used in heating mode.

[nike123]

Thanks a lot Nike 123, this was exactly what I was looking for. However someone mentioned there can be problems with "scaling" i.e formation of limestone and/or gypsum on the heat transfering surfaces in the plate heat exhanger when producing hot water above 65 degree of Celsius. Perharps you should use some other kind of exhanger?

Generaly, I use desuperheater in closed loop with hot water tank heat exchanger.