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Thermal Space Temperature unaffected by Sensible Cooling of VRF

asked 2015-04-26 16:23:22 -0500

eklein12's avatar


I am modeling a single room that is cooled and heated by a VRF system. It has one outdoor unit and is connected to two indoor units that cool and heat the space. I have set up both units so that they begin cooling at 80 degrees F and begin to heat at 68 degrees F. The VRF system does begins cooling when the temperature goes above 80 degrees, but the rate at which the temperature increases seems to be unaffected. This is shown in the pictures below. I am unsure of why this is. Is the cooling capacity not large enough? I am fairly new to energy plus so any advice on how to trouble shoot this issue would be much appreciated.

Thank you!

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I think we would need to look at the particular model to figure out this one.

Kyle Benne's avatar Kyle Benne  ( 2015-04-30 12:33:39 -0500 )edit

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answered 2015-07-22 20:19:05 -0500

These results do indicate insufficient capacity to meet the load. Notice how the power falls off rapidly when the temperature is maintained at 26.7 C (80 F) and then falls below 26.7 C indicating that the load is also reducing. Without seeing the model inputs, I would recommend increasing the system capacity to see if that helps. Report back with the impact of this change.

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answered 2015-07-23 07:15:29 -0500

Chris Jones's avatar

updated 2015-07-23 07:21:22 -0500

In general: Q = 1.08 * cfm * dT or DT = Q / (1.08 * cfm) So the change in temperature in the space is determined by both the cooling capacity and the supply flow. Sometimes increasing just the cooling capacity is won't solve the umnet load issue.

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Matthew, how do you find the time?

Chris Jones's avatar Chris Jones  ( 2015-07-23 07:48:47 -0500 )edit

Simple, @Chris Jones, I just decrease my time step ; )

MatthewSteen's avatar MatthewSteen  ( 2015-07-24 08:06:17 -0500 )edit

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Asked: 2015-04-26 16:23:22 -0500

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Last updated: Jul 23 '15