HVAC System: Heating Details - Supply Water Temperature Input not Registering


#1

I’m having difficulty assigning a custom supply hot water temperature to the HVAC System component via the heating details. Regardless of the temperature input, the supply temperature in the IDF file remains 82C. Has anyone else had this issue before, and if so, how can it be fixed? Thanks.

Model Details:
openstudio-2.7.0.
EnergyPlus>9-0-0
HVAC System Template: Fan Coil Units + DOAS


#2

I believe I can answer my own question here, but it would be great for others to confirm.
Adjusting the Supply Water Temperature within the Heating Details component sets the supply water temperature within the Hot_Water_Temperature schedule used by the loop setpoint manager. The zone equipment and heating plant “Design Water Temperature” fields will still read 82C, but the setpoint manager will ensure that water is supplied to the zones consistent with what the user specifies through the Heating Details component.


#3

@MichaelEsposito ,

Yes, your explanation is correct. The “Design Water Temperature” property does not really affect the temperatures experienced in the simulation. It is just a property of what the system is designed to handle and not how it actually ends up functioning at over the course of a year. So you can build a system to handle temperatures of 82C water but you actually operate it at 50C. Changing the “Design Water Temperature” may affect some curves used to describe some of the HVAC equipment but, unless to change it to a totally nonsensical value, I have usually found that it does not affect the simulation in a noticeable way.

BTW, you can always verify that the supply temperatures are what you expect by requesting node-level temperature results from a simulation like so:


NodeLevelResults.gh (544.9 KB)

Typically, HVAC systems have a lot of nodes (even when it is only serving a single zone) so be prepared to import a lot of data into Grasshopper if you do this. Also, to make sure that you are looking at the right part of the HVAC system, you probably want to open the .osm in OpenStudio, go to the HVAC tab, and click on some of the different nodes to make sure you select the right node number from the data tree of all temperatures that you get when you request node-level results.


#4

@MichaelEsposito
If you are familiar with openstudio hvac, you could build your own system:FCU DOAS.gh (84.7 KB)

In terms of supply temperature, as @chris mentioned, requesting node-level temperature result is one solution, but this is going to be a lot of data without specifying the node name.
There is an easy alternative, you can request the “Plant Supply Side Outlet Temperature”, which will be the water temperature that pump into the coil.


#5

Thanks @MingboPeng and @chris.

To provide a little more context to the question, the goal is to track unmet heating hours as one reduces hot water supply temperatures from 180F down to 120F. To do this, I am imagining that coil/radiator heating capacity (as sized for 180F hot water) would be fixed for all cases.

@MingboPeng, On a separate but related note, I’ve been having issues loading two Ironbug components in particular and exporting detailed system requirements to OS (see attached images). I wasn’t able to find any forum discussions on this topic. Could there be a compatibility issue between the latest Honeybee release, openstudio-2.7.0, EnergyPlus version 9-0-0, and Ironbug?

Ironbug%20Loading%20Error


#6

Hi @MichaelEsposito
OpenStudio 2.6 and 2.7 have some bugs haven’t been fixed, both Honeybee and Ironbug won’t work with all system types with 2.6 and 2.7.

OpenStudio 2.5.0 (note: not 2.5.1 or any above) is still the suggested version to use with Honeybee.

HVAC Template has been included in the new version of Ironbug, please update it from: https://github.com/MingboPeng/Ironbug/releases


#7

@MichaelEsposito ,

I also wanted to add that nearly everything in the basic honeybee templates is autosized by default so, if you want to hard size the heating coil, you will either have to use the Ironbug components (I think @MingboPeng has built in some inputs for this) or you would have to write a short OpenStudio measure to do it for you.