design chiller delta T

[moideen]

When design chilled water system for new buildings, the old method was 10F delta T. in these days chiller delta T considered above 12F. The chilled water pump size can be reduced by this design method. My question is that, is there any other benefits? thank you

 

[SAK9]

Please have a read through this article. It demonstrates how little benefit is derived from higher chilled water temperatures. However in a very large system some capital cost savings may arise from smaller pumps, smaller pipes, valves etc. but be mindful of the increase in cost of chillers, AHU coils etc.

http://www.mcquaytw.com/Engnews/Engineering_14.pdf

 

[ChasBean1]

Good question with a lot of variables involved in the answer. SAK9, your link didn't work for me, but based on your description seems like it would be an interesting read.

 

[SAK9]

Chasbean I have uploaded the pdf file to this post. It is indeed an interesting topic. For any energy efficiency improvement HVAC system must be looked at in its entirety. You can not improve efficiency of water distribution by lowering chilled water temperature as chiller efficiency goes down. It is like robbing Peter to pay Paul

 

[BronYrAur]

Chiller delta-T should match AHU coil delta-T or other process delta-T. Many chiller plants are designed with large delta-T's, but then they are connected to old distribution systems with low delta-T coils, etc. The plant never sees its design delta-T. So as others have indicated, the entire system must be considered.

 

[moideen]

BronYrAur :when high deltaT Connected to low deltaT ahu/fcu leads to problems,ok then low deltaT chiller connected to high deltaT ahu/fcu, what will happen to the performance? thank you

 

[BronYrAur]

Remember that a flow and delta-t is one operating condition of any machine or coil. Change the flow or change a temperature, and you will have another operating condition. There are many possibilities. But to zero in on your question, if you have a high delta T coil and only a low delta-t chiller, you may not be able to satisfy the load of the coil. You would have to attempt to push more flow through that coil, which may or may not be possible. Same thing with the chiller. More flow through a chiller will give you a lower delta T but not necessarily a lower capacity. You may very well get a higher-capacity. It all depends on your delta T.

Delta T on an air handler coil for example is limited, because you also have to consider the air temperatures on the other side of that coil. If you're entering air temperature is colder than your desired leaving water temperature from that coil, there's no way you will get the delta-t on the water side that you want. So it's always important to consider the entire system. And remember that your design condition only exists for a very short time during the year for a typical HVAC application. You need to select equipment that will perform during the mon peak times.

 

[HVAC68]

If it is not a big project, then the projected savings on account of lower pipe sizes, pumping, etc., may not be much and/or may not be favourable. However, this works well for large plants bordering on district cooling type of installations.


HVAC68

 

[lilliput1]

You would need to check performance of existing coils to see if they could be made to have 12 degrees temperature drop (instead of original 10 degree design) with 2 degrees colder supply water temperature and still get the same air sensible heat cooling performance. In large installations when new load is added at a location remote from the chiller plant it may be possible to add more chiller capacity without having to increase pipe size by lowering the chilled water supply temperature so existing coils would require less gpm freeing the excess gpm to serve the addition.