Chilled water vs DX HVAC

[Graybeard]

Over a 10 year period which is better CW-HVAC or DX-HVAC?
For our application is "cold recovery" economically viable?

We have a large plant in the Southeast with several Chilled Water systems that supply CW to our buildings for HVAC. We are planning to build a new metal building 40x60' with 30' eve. Building will have a process load less than 50 kW. HVAC will use 100% makeup with vent rate of 1 scfm/sf floor area. Since as a general rule we use chilled water for HVAC our suck and blow boys insist on using chilled water, but since none is available in this area of plant they want to spec a dedicated package chiller. Part of their logic is based on the fact that they say DX systems don't like to reduce 95F air down to 60F. We need to maintain a max temp of about 80F. To me a dedicated CW system seems too complicated and DX seems the way to go, but I can't address the 95-60 issue. Also, I can't get them to consider "cold" recovery on the 2400 cfm of 85F air we will be exhausting. They say it is cost prohibitive.

 

[PacificSteve]

For this size and load, I would agree that a chillwater would be more expensive and complex, with no real energy savings compared to package unit, if it is an aircooled chiller we are talking about. A water cooled would be more efficient on electricity, say 30%, but I haven't seen any economically effective system in your small tonnage range. Normally, 100 tons would be where you would start considering water cooled, but that depends on your rates for water and electricity, also.

Multiple package units in the 15 ton range would seem like a natural choice, cause I guess it isn't 95 all the time, and the part load operation of a single large package unit is probably not all that good in reality (as opposed to the books). Why do you need 100% OA?

Heat or cold recovery tend to be expensive, and salemen related to same are unlikely to provide enough factual data to make a proper decision, especially if you have opposition.

However, a proper decision would be based upon your energy unit cost, and the efficiency of your new AC system. Without knowing these, it is impossible to go forward. I would lean towards the "its not worth it" attitude, however with your 100% OA, it could be worth a real look.

 

[Graybeard]

I'm not sure where the 100% OA is comming from, except for the 1cfm/sft air change rate. I havn't done a calc. but i'm guessing that majority of cooling load is to condition that air, so no need for recirc. The high air change rate is due to industrial hygene reqs. for the area.