Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question

Constant vs variable flow - Condensation loop

asked 2022-02-22 15:15:17 -0600

obuchely's avatar

updated 2022-02-22 21:00:03 -0600

A potential customer has a core & shell building with packaged water source system (cooling only) connected to a constant water flow cooling tower. The cooling tower fan has variable speed. The internal untis are not part of the scope.

They want to change the system since it is old. One of my alternatives is to change the cooling tower for a new one and implement variable condenser water flow. One of my colleagues has suggested me that controlling variable condenser flow is not easy and will bring more problems than solutions. I am thinking to implement primary and secondary condenser loops. The primary will have constant water flow and will be connected to the cooling tower. The secondary loop is going to be a close loop with a heat exchange with the primary loop. The secondary loop will serve the packaged water source units and will have variable flow.

Does anyone have experience with this system implementation?

I am trying to simulate the two scenarios in Openstudio but I think it won’t give me the outputs that I am looking for.

Any comments will be appreciated.

edit retag flag offensive close merge delete

1 Answer

Sort by » oldest newest most voted

answered 2022-03-16 13:56:18 -0600

Keigo's avatar

At first, as long as I know, we can't model variable condenser flow in EnergyPlus. Please refer to this post. I also wanted to compare constant flow and variable flow, but I couldn't.

In my experience as a MEP engineer, I have designed both constant condenser water flow (variable fan speed) and variable condenser water flow (constant fan speed), but in both cases, the plant system is not the packaged water source units but absorption chillers. It is best to ask the manufacturer of the packaged water source units. For some packaged water source units, the range of condenser water flow rate is limited such as 80% to 120% of the rated flow rate.

There are various factors involved in the energy saving of the whole plant system, so it is not clear which scenario saves more energy, but in your variable flow system with primary and secondary loops, primary loop is constant and adding plate-type heat exchanger increases pump head, which sounds disadvantageous.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer


Question Tools

1 follower


Asked: 2022-02-22 15:15:17 -0600

Seen: 243 times

Last updated: Mar 16 '22