making a chiller with brazed heat exchanger for cond and evap

[pardal]

Hi all HVAC experts.

I had a background of 30 years doing havac servicing , now I want to make a 12 ton chiller water condensed using both evaporator and condensator brazed heat exchangers.
The chiller is to be used for HVAC comercial 7 ° C leaving 12° C return chilled water
Water temp from cooling tower will be 34 incoming to heat exchanger out 37 ° C to tower.
Up here I had all the tips solved , what do I need is to know .
Best way of temperature control .

Closing liquid line and let the compressor stop by low pressure .

Or shut off compressor by thermostat

And the most important and my big doubt .

How to cal the liquid reciever to allow the dampen function of the circuit.

Yet I had choose the compressor for 12 TR
and the two exchangers, expansión valve filters presostats an so on.
Thanks in advance.

Pardal











Pardal

 

[VEEKRISH]

Pardal, I have my reservations on using BP Heat Exhanger on the Cooling Tower circuit. Please remember that there is no way to de-scale or clean the Heat xchanger. There is a problem on the Evaporator too, but the situation is not so serious (provided you ensure that water quality is good and it is a close loop system).

It is always a good idea to have a suction pressure cut off. So that no liquid flood back occurs if re-start occurs quickly.

What type of compressor are yoiu using?

 

[pardal]

Hi veekrish, thanks for your tips.
I will use a bristol reciprocating compressor rated 144000 btu.
Pardal
Pardal

 

[VEEKRISH]

Hi Pardal,

OK, so is the BRISTOL Recip you are planning a multi cylinder compressor ? Does it have facility for unloading the cylinders ? If it does, then you can use that as a form of capacity control too. as temperature reduces (reducing load), the cylinders begin to unload. Check it out.

 

[pardal]

The Bristol is an hermetic compressor.

Pardal

 

[VEEKRISH]

Do you really need a receiver ? Refrigerant pipe lengths will not be large, considering you are using a water cooled system. If there is no part load operation, perhaps you can do away with the receiveer altogether. Ofcourse, if you want to still play safe, use a small tank (about 25 % volume of the refrigerant). that should be OK

 

[pardal]

thanks.

Pardal

 

[ClydeMule]

PArdal,

Thanks for your tip on the coiled HXR.

We have been building chillers for 40 years or so. We cut off the compressor by a thermostat. We mostly build air cooled chillers, but for water cooled chillers, we used Packless COAX condensers. We are moving from bare tube coils to brazed plates on the evaporators. As VEERKISH stated, fouling of a BP on a tower can be a concern. COAX condensers are also not cleanable, but we have never had a fouling problem. Brazed plate passages are much smaller so it is more of a concern.

To keep the compressor cycling under control all of our systems incorporate a reservoir inside the chiller. The 12 ton has a 100 gallon tank. Or you can use hot gas bypass. If you do this make sure you use a brazed plate that doesn't use an internal distributor.

We put receivers on everything. Since BP condensers and COAX condensers don't have a lot of pump down capacity, it is convenient to put one in.

Based on your conditions you would probably be ok selecting components based on nominal sizes.

One other thing, a flow switch on the evaporator is key. A freeze stat doesn't always react fast enough. If you can, a time delay on the flow switch is handy to prevent nuisnace trips.

Good luck?

Clyde

 

[pardal]

Hi Clyde : about the tip , it was only a simple way to do .
And as the pipe will be sumerged in water , overheating is not a problem.
About fouling on BP exch , I had used it with a high water purge at the cooling tower , so I can control the salt concentration. I must told you that we had no problem about how many water we spent. An it is cheaper than treating the water.
I put two filters , one at pump suction side , a big one about 200 mesh . to avoid any debris.
An other on each BP exch nominal pipe zised , and do a piping so the flow pattern can be reverted so it is easy to get out any debris or small particle .
About coaxial vs PB exch descaling , I had a big trouble once with coax because ther are dead zones where the descaling fluid could rest without being rinsing and it punchture the refrigerant pipe , it was a big luck that we new it before the water pressure never comes higer than the gas , so no water come inside the refrigerant pipe.

The 12 ton has a 100 gallon tank , is for water, I guess ?

We put receivers on everything. Since BP condensers and COAX condensers don't have a lot of pump down capacity, it is convenient to put one in.

I read at SWEP site that punp down shall not be used.

One other thing, a flow switch on the evaporator is key. A freeze stat doesn't always react fast enough. If you can, a time delay on the flow switch is handy to prevent nuisnace trips.
I agree totally , I used both , and the freeze stat with reset , so I can check any fault .

Remenber my e-mail if you want to direct contact







Pardal