Morteza's profile - activity

Thank you for your suggestion, Supply Air Fan Operating Mode Schedule Name was “Always On Discrete” in PTAC and was blank in PTHP so I added the same schedule for PTHP. Now the fan energy consumption is the same in both of the OSM models. Thank you all for your time and your help in this issue.

As you have mentioned, the PTHP fan in OpenStudio consumes far less energy. This is the main reason for the energy consumption difference of the PTHP in two engines. As you can see in the following screen shots above entry for both of the models are the same, but the annual energy consumptions are very different!

This is true and in this experience the simulation results in both of the engines approved it too. However, in heating dominated climate zones (i. e. Zone 4A) and for heating dominated building types (i. e. residential buildings) changing PTAC to PTHP may increase the annual energy cost to a certain level, which depends on heating efficiency of the two systems. This is the effect of the difference between costs of different sources of energy. PTAC uses gas for heating, which is cheaper than the electricity, but PTHP uses electricity.

I revised all the data entries in all of the models. Now all entries including system efficiencies of PTAC and PTHP systems comply with ASHRAE 90.1-2007. The default rated cooling COP for PTHP was 5 in OSM and 3.2 in eQUEST, revising this value increased the annual energy consumption of the OSM model. In addition, the energy cost related to DHW was not included in the OpenStudio models. With these changes, the differences between the annual energy consumptions of the identical models in different engines are reasonable, but my original question is still there; in EnergyPlus engine PTHP is more energy cost efficient than the PTAC but in DOE-2 engine it is the opposite. I think EnergyPlus engine (the default values for the system) assumes PTHP much more energy efficient system than the PTAC. Following is the summary table of the simulation results.

Yes I did, please refer to the answers part

@Julien Marrec, I think as @ljbrackney pointed out it is the result of different approaches between the two calculation engines. I am struggling to find out why with EnergyPlus simulation engine PTHP system is more energy cost efficient than PTAC but in DOE-2 engine it is the opposite.

@pflaumingo, thank you for your comment, I will check all the entries in both of the models one more time and will wait to hear more from you.

@pflaumingo, thank you for your comment, I will check all the entries in both of the models one more time and will wait to hear more from you.

@ljbrackney, thank you for your comment and the provided information, finding in this thesis paper is very helpful; I will study the whole paper.

I am studying annual energy costs of two baseline models for a LEED residential building, PTAC VS PTHP. This is a 9 story building in Washington, DC and to simplify the process just created a bulk model per ASHRAE 90.1-2007 energy modeling requirements.

Keeping everything the same in two models except the HVAC system, simulation results per eQUEST version 3.65, built 7163 indicate changing PTAC to PTHP will increase the annual energy cost from $219,597 to $236,476 (-8.1% annual energy cost savings). This was the results that I was expecting based on my previous experience.

Surprisingly, when I use OpenStudio-1.12.0.ef50b89958-Win64, simulation results indicate changing PTAC to PTHP will decrease the annual energy cost from $102,130 to $117,449 (13% annual energy cost savings).

In short:

• In eQUEST, changing PTAC to PTHP = 8.1% annual energy cost increase
• In OpenStudio, changing PTAC to PTHP = 13% annual energy cost savings

following are links to files of this experience. I would appreciate it is someone would review these models and let me know the reason(s) of this contradiction.

• eQuest
• OpenStudio

@MatthewSteen I am using Sketchup 16.0.19912 and OpenStudio 1.11.3 and do not see OS:ElectricalEquipment object in the inspector of SketchUp Plugin. Was this object removed in the newer versions or I am missing something?

Thank you very much for your response. This process works, I can get the expected energy consumption related to SHW.

I still need some advice on this subject. When you set the Max Loop flow rate to 20 GPM and run the model what was the percentage of annual SHW energy consumption compared to the whole building annual energy consumption? In my model, the Max Loop Flow Rate is 47.137 gpm and annual energy consumption of SHW is only 2% of the annual energy consumption of the building, which is not realistic. With the same fixture definitions: lavatory faucet 2.2 gpm, shower 2.5 gpm and kitchen sink 2.5 gpm I changed the Max Loop Flow Rate to Autosized, but this did not change the simulation results.

Thank you very much for your help, your guidance solved my problem. I revised the peak flow rates of the fixtures in Loads tab per total building flow and simulation results showed the expected values.

Julien, thank you for the confirmation and additional information, the only purpose of selecting a space name for the water use equipment was to use multiplier (total number of the residential units), is there other way(s) to select multiplier for water use equipment?

Julien, thank you for your response. I am not quite familiar with creating measures, so thought using following procedure to model SHW for the apartment units of the model: 1. Create a new plant loop with a water heater and water use connections 2. Select an unconditioned space in the underground parking garage that is not part of the building total floor area 3. Select a multiplier equal to the number of apartment units within the building for the Thermal Zone of the selected space. 4. Select this space as “Space Name” for each of the Water Use Equipments Is this procedure correct?

@Julien, thank you very much for the helpful information, I will study these options carefully. However, I did not find any measure for service water heater in BCL library, could you please provide a link to this measure? In addition, this is a LEED project and the baseline model should be consistent with ASHRAE 90.1-2007 modeling protocol, hence I have to provide answer to the entire question that you mentioned from the standard for the baseline model, is this correct? Thanks again for all your help!

What is the best way to model Service Hot Water for a MidriseApartment in OpenStudio? Assuming each apartment unit has its own water heater, is it more appropriate to select separate water use connections and water use equipments for each of the apartment units, which is very time consuming, or is it okay to select a water use connection for a group of the apartment units located in each floor or in the whole building?

@David Goldwasser, Thank you very much for your help, I used OpenStudio 1.11.3 with new intersect measure, and did not encounter any error.

@David Goldwasser, thank you for your time. The OSM file was sent to OpenStudio@NREL.gov

I am using OpenStudio 1.11.0 Build Number: 4313b0e0d9.

In this model, a ‘subsurface’ was surrounded by a single larger surface by more than two edges. After I divided this surface in two and re used the surface matching in OpenStudio encountered no error and surface matching was successful.

I tried to use surface matching measure for my model per David Goldwasser recommendation, but before the execution of the measure encountered following error:

Your help would be greatly appreciated!

How can I assign Air Inlet and Air Outlet Nodes to the model? This is a midrise apartment project so I have selected PTAC with HW heating for the baseline model. I also have created a hot water loop and an air loop (following screen shots) but when I run the project, encounter following errors:

Error detected in Object=COIL:HEATING:WATER, name=COIL HEATING WATER 1 * ~~~ * Field [Air Inlet Node Name] is required but was blank

Error detected in Object=COIL:HEATING:WATER, name=COIL HEATING WATER 1 * ~~~ * Field [Air Outlet Node Name] is required but was blank What is the solution? Thank you for your time,

C:\fakepath\Air Loop.jpg

Thank you for your time!

To comply with LEED requirements on supply and return fans “Baseline supply and return fans operate continuously when spaces are occupied and cycle when unoccupied” I think for PTAC systems, in addition to creating a schedule, one need to set the “Outdoor Air Flow Rate When No Cooling or Heating is Needed” to “0”, is this correct?