Energy conservation of Chillers 1

[coolbug]

Dear all,

Kindly help me in solving the following problem:
Preface: There is a water cooled chiller which is used to send the chilled water to 15 AHUs. Each AHU works for a clean room, where drugs(Active Pharmaceutical Ingredient) is made.
Facts: 1. The chiller capacity is 189 TR and the connected motor is of 125 kW power.
2. Each AHU is drawing different amount of chilled water depending on the design capacity of that AHU and the requirement of the Clean room.
Problem: As of now the Chiller is working 24*7 irrespective of the processing of drug going on or not in the clean rooms. So now we are planning to reduce energy consumption. Depending the orders of the drugs the Clean rooms work; if there is no order then they stay idle. So most of the times all the Cleans rooms are not running and it so happens that 4 or 5 (alternately) out of 15 stay idle at nay given time. So now how to save energy as Chiller can not be shut down even if 1 Clean room (and in turn 1 AHU) is working???
Constraints: AHUs can not be shut down as they are crucial to maintain pressure and control contamination. If closed then it will require a validation for 7 days. AHU shut down not preferable.

 

[KiwiMace]

As a starting point:

If any of your AHUs require chilled water, then you have to run your chiller. You can save energy in the operation of the chiller with such things as a VSD compressor, unfortunately this and most other options are design time decisions and retrofit is not always economical.

To save energy in your pumping (assumption: you appear to be describing an existing constant flow system) you can change to a variable flow system - change your AHU valves to 2-way type and install VSD pumps to distribute from your chillers. There is a chance that you can do variable primary flow, but this depends on your existing chillers, but it will be cheaper to retrofit.

You can install vfds on your AHUs and ramp down the airflow saving fan energy. Your pressurisation scheme and validation reasons above may not allow this though.

This problem requires a good consultant with Pharma experience.

 

[coolbug]

Thanks Kiwimace,

But we cnt change the air flow from the AHUs coz same air flow with 20 changes per hr is the mandate.
We also have thought about instaling inlet and outlet valve on the AHU coils so that when that AHU is not in use, the valves will be closed down. that will reduce load on the Chillers but not lead to much energy conservation.

 

[urgross]

I'd recommend looking at the Labs21 web site, as many of the same strategies for energy savings could apply to clean rooms. As the ACH is constant, is temperature/RH reset during unoccpied periods acceptable?

Kiwi has a good idea in placing PICV's on the cooling coils and placing a VFP on the primary or secondary pump. How are you controlling chilled water supply temperature?

I'd consider VFD's on the AHU's and exhausts to maintain flow aginst loaded filter, and minimizng exhuast to 20 ACH and minimizing volume flow to minimum to reach required dP across secondary containment. Pressure independent air control valves with master-slave differential flow between supply and exhaust works well and is used frequently in lab and medical facilities.

Unoccupied sensor for lighting might interlock with HVAC temperarue reset.

Low pressure filters might save on fan energy. Fan motor selection may also be a chance for savings. ASHRAE has a good journal publication on this, and TAMU has a real good article on air side energy savings for clean rooms.

Any possibilities for sensible heat recovery? Is recirculation allowed in meeting cleanliness level?

Lots of very good literature available, you just need to google.

 

[SAK9]

As Urgross suggested,having a broader temperature band/RH Band for the unoccupied rooms looks likely a good solution. This may allow you to reset the chilled water temperature. But this is possible only if you are in a dry climate.Dehmudification of pressurization/ventilation air is very critical in pharma applications.Also look at options like free cooling on the water side if climate permits.

 

[Drazen]

you should tell us what else is mandated, that limits number of alternatives and makes choice easier.

i have worked on pilot pharma plants long time ago and cannot recall by heart, but do remember that there was myriad of requirements.

shut down if tuff because of need for re-validation, but are you sure that it is not possible to use recirculated air during unoccupied periods? system cannot "know" which air is used, and even if you are using some ppm measurements i doubt outdoor air reading would differed much from readings of recirculated super-filtered air during unoccupied period.

 

[RossABQ]

Personally, I think it could get pretty expensive to do this right. Replace the (centrifugal?) chiller with a 3 or 4 section chilled water unit that sequences on sections (compressors) in 50-ton increments. You can turn down centrifugals quite a bit but it's tough to beat a bunch of smaller units, especially since it gives you some redundancy.

 

[coolbug]

Replacing option is too expensv...and i cnt suggest that to management..Also load is 60-65 % of most of the AHU and for few its 85%.
Reciculation of air already takes places aftr the outlet air passes thru Air filters is 10 micron.

 

[coolbug]

Dear All,
I am novice in diz field, so kindly help.
I now want to calculate the power saving. The connected motor with the chilled water chiller is of 125 KW capacity helping it in generating 189 TR (needed for working of 15 Clean Rooms). Now suppose that due to no orders in place at few clean rooms can be shut down , and in turn the respective AHUs inlet chilled water valve is closed. So I guess, this will ensure that the load of the Chiller is reduced by the amount of TR requirement of that AHU.
So now can u tell me how to calculate the estimated reduction in power consumption due to reduced load (caused due to closing of AHU inlet valves ).......?

 

[willard3]

Forum policy:

>>>>These fora should not be used to bypass your own in-depth research on the issues that affect you, nor is it intended to be a substitute for appropriate professional assistance within your field or geographical region.

It sounds like someone where you work has asked you to model this and, This is not simple. Hire an Engineer who does this to find the energy reduction. Cooling tonnage is proportional to KW.