Retro-fitting cooling, sizing q's

[John MacK]

Hi Guys,

I'm trying to give a customer a quote for retro-fitting cooling into existing air-handling units.

I can get the coils (either DX or CW) from the unit manufacturer, my main problem is sizing the chiller or condensing unit, and deciding which to use.

The cooling coils have a capacity of 126Kw and 165Kw, is that the size of chiller I need, i.e one 290Kw chiller doing both systems or one 126Kw and one 165Kw ?

One of the reasons for asking is that there is other plant on the site which has chilled water cooling, about another 6 AHU's, and the chiller for all of them is just 250Kw capacity.

Any opinions on whether to use DX or CW welcome also.

[Samarjit Sen]

As you are retro fitting the Cooling Coil only, first see if the existing system is chilled water or DX system. Secondly find out the details of the fans of the AHU's.

What is the rating of the Compressor, based on that you will have to have the total Cooling Coil rating. It would be much better to find out the heat load of the areas which the AHUs are catering to and based on the same select the coil capacity.

[John MacK]

As you are retro fitting the Cooling Coil only, first see if the existing system is chilled water or DX system. Secondly find out the details of the fans of the AHU's.

What is the rating of the Compressor, based on that you will have to have the total Cooling Coil rating. It would be much better to find out the heat load of the areas which the AHUs are catering to and based on the same select the coil capacity.


As I said, there is existing chilled water.

As I said the AHU manufacturer has selected the coils they would have been fitted to the units based on the original design criteria (if they had been asked to supply cooling coils to these two units), they have also advised about changing the fan motors and the drive pulleys. I am presuming therefore that the heat loads are 126Kw and 165Kw.

[Brian_UK]

Personally I would go with chilled water.

1. You already have it on site so it is familiar to existing staff.

2. The refrigerant charge size on site can be smaller than DX systems. Things to be considered when leaks occur or need to be checked for.

3. The main cooling plant is contained in one area.

4. If possible then the two systems could be linked together and then provide some backup in the event of any plant downtime.

5. Chilled water pipework can be run in ABS which may be easier than copper to run in.

[Carlos Barrantes]

First , a Load Calculation should be done at different hours and date .
Considering a Diversity Factor of 0.8 , you need 80% of 126 more 165 Kw , that is to say , one 230 Kw Chiller

[John MacK]

Thanks for the replies.

Due to locations there is not really an option of one chiller doing both units.

If I installed a chiller and did the pipework in ABS would it need to be insulated or have trace heaters fitted?

[Brian_UK]

If I installed a chiller and did the pipework in ABS would it need to be insulated or have trace heaters fitted?Definitely insulate the pipework; trace heaters would possibly already be fitted to the chiller - assuming that they were asked for.

You might want to run a low glycol mix to provide additional frost protection.

[Electrocoolman]

Not sure what your airhandlers are conditioning, but is it worth considering a heatpump unit to provide some heating during the rest of the year?

I've used ABS pipe successfully...you can get different grade/wall thickness. With the thicker grade, and depending on the temperatures and length of pipe run, you can possibly get away with no insulation indoors.

[nike123]

Does anyone of you guys using PPR pipes like this:
http://www.fusiotherm.com/?id=307
I using them lately with great success.

What is difference between them and ABS pipes?

[Electrocoolman]

Hi Nike,
Looks interesting.....how much is the tool for heat welding the joints, or do you hire (rent) it?

ABS is solvent cleaned then solvent weld, but you must then wait +24hrs before pressure in pipes.

I'm not sure what the temperature limits for ABS are, as I've only used it for chilled.

[nike123]

There are several tools for different pipe sizes. The smallest tool for pipes up to 50mm is about 200 pounds and Teflon heads are from 20-50 pounds. For larger diameters we rent tools.