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Extraneuous PIU system central heat coil output

asked 2014-10-21 11:42:52 -0500

updated 2017-09-02 14:55:43 -0500

Hi all,

I am modeling a PIU system w/ a water-cooled DX coil and series electric FPBs; no central or preheat heating coils. Using eQ v3.64, but have also observed this in eQ v3.65.

SV-A report indicates heating capacity for system is 0.

Despite this configuration, hourly reports of for SYSTEM, 'Total central heat coil output (Btu/hr)' indicates there is varying amount of central heat energy output in the first 1-2 and in some cases, the last 2-3 hours of many days in heating months (location Seattle, WA). This is also confirmed by looking at the difference in energy reported between SS-A Heating and SS-B Zone Heating. It is not necessarily a trivial amount of energy, ~10-25% of total system heating in two models I've tested.

Have others observed this before, and if so, found a way to fix this?

Can't say I've tried everything I can think of, but this is what I have tried:

  1. Specify HEAT-SOURCE = "NONE" and leave HEAT-SET-T undefined
  2. Set HEAT-SOURCE = "ELECTRIC" and use a very small capacity both -1 or -1000
  3. 2 + setting HEAT-CONTROL = "CONSTANT"
  4. 3 + set HEAT-SET-T various values, including minimum (50F)
  5. Setting HEATING-SCHEDULE to something that locks out heating. This works, but also locks out zone heating, so not a viable solution.

Thanks in advance for any input.

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answered 2014-11-17 16:51:06 -0500

I played with your model some and did find a possible solution, though probably not ideal. I set the Heat Source to "Hot Water Loop" and created a Hot Water Loop for just that coil with a boiler as the source. I went into the Loop Properties and the Operation tab and changed the Loop Operation to "Scheduled" and set the Heating Schedule to a schedule set to 0 all the time, keeping the loop off year-round. Looking at the output report for SV-A, the Heating Capacity is 0 and looking at the hourly report, the "Total central heat coil output" stays at 0 through the whole year. I didn't go into great detail to make sure there aren't any other effects you may not want but it's worth a try.

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This is a good suggestion; thanks for taking a look at it.

DavidReddy gravatar imageDavidReddy ( 2014-11-17 17:37:09 -0500 )edit

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Asked: 2014-10-21 11:42:52 -0500

Seen: 459 times

Last updated: Sep 02 '17