EnergyPlus ASHP modelling errors--Plant temperatures are getting far too cold

asked 2015-09-28 12:46:56 -0500

updated 2015-09-30 10:46:36 -0500

Hi all. I used the new beta version of DesignBuilder to model the ASHP detailed HVAC system.

image description

The ASHP will be used for heating and Hot water. I upload the HVAC system as shown below.

error I got: Last severe error=Plant temperatures are getting far too cold, check controls and relative loads and capacities

*** * Warning * Plant loop falling below lower temperature limit, PlantLoop="AUX HW LOOP"

*** * ~~~ * This error occurred 5 total times;

*** * ~~~ * during Warmup 5 times;

*** * ~~~ * during Sizing 0 times.

*** * ~~~ * Min=-136.598068

* PlantLoop Outlet Node (SupplySide) "AUX HW LOOP SUPPLY SIDE OUTLET" has temperature=-111.1 {C}*

I think this is the place where the error occurred, however, how can I increase the supply side outlet temperature?

I've checked the minimum loop temperature is set to 0 and the maximum loop temperature is set to 80. When I tried to increase the minimum temperature from 0 to 20, the error message changed: Min=-56.215634 and the error occurred times increased to 146.

I have no idea where this -136 degree come from.

Thanks for your help. Thanks again.

answered 2015-09-30 01:44:16 -0500

Andy Tindale
121 ●3 ●2

ASHP systems can't be autosized so you should check the rated heating capacity of the air to water heat pump coil. The default value is designed for a fairly large building (40kW) and you may need to decrease this. I don't think that oversizing will cause this problem though.

Did you use the "ASHP Air to water Heat Pump convector" template? This works for me without modification when applied to the test house that comes with DB.

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Hey Andy, thanks for your answer. I double checked with the heating capacity, it is 40kW indeed. I used ASHP air to water heat pump, water convector template with the default settings, didnt do any changes.

Any suggestions?

nancynanxiaodan ( 2015-09-30 09:07:04 -0500 )edit

If you post your model I'll have a look to see if anything jumps out as being wrong. I don't know if attachments are allowed on unmet hours but if not then please send it to the DB support desk.

Andy Tindale ( 2015-09-30 09:29:59 -0500 )edit

Hey Andy, thanks for your kind support, I could not upload attachments for some reason on unmethours, however, I did submit a ticket on DB support desk, and the ticket number is #QHW-497-34562. Thanks in advance!!

nancynanxiaodan ( 2015-09-30 10:58:37 -0500 )edit

Hey Andy or Nancy, Was this ever resolved? I'm having the same issue with a loop created to serve zones using Water To Air Heat Pumps in OpenStudio.

Charlie Stevens ( 2016-12-07 16:34:36 -0500 )edit

Hey Charlie, we've been successfully using ASHP systems in DesignBuilder. Provided the control settings are made correctly it should work well. You may find the DB v5 help and notes useful. As mentioned in my original reply getting the capacity of the system right is important and as the help notes say the setpoints must all be set up right.

Looking back at Nancy's ticket on our support desk she was able to resolve the issue by re-importing the ASHP HVAC template using a production release version.

Unfortunately I'm not familar with the OS HVAC GUI so can't help with that.

Andy Tindale ( 2016-12-08 04:39:15 -0500 )edit

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