Question-and-Answer Resource for the Building Energy Modeling Community
Get s tarted with the Help page
Ask Your Question

Energy Conservation during Unoccupied Hours

asked 2021-06-30 13:00:41 -0500

Ahmad gravatar image

updated 2021-07-01 12:19:20 -0500


I'm using Openstudio to implement energy conservation measures to my building model. The building is actually an advanced one which has room occupancy sensors and also a building management software for the equipment. It has an absorption chiller for cold water supply and a boiler for hot water supply to the AHUs and FCUs installed.

The building is actually consuming half of its energy during occupancy hours (From 8 am till 8 pm) and half of its energy during un-occupancy hours (8 pm till 8 am).

I'm modeling some energy measures that I could think of which are: Replacing double glazed windows with triple glazed ones, lightning replacements to decrease lighting loads, reducing electric equipment loads at night, modifying HVAC setpoints during un-occupancy, and even turning the HVAC system off during un-occupancy.

The roof insulation is properly structured, so no need to modify anything to it. The installed pumps are all Variable Speed pumps.

I'd like to take your thoughts on any other measures you can think of.


edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted

answered 2021-06-30 16:43:55 -0500

sashadf1 gravatar image

updated 2021-06-30 16:44:11 -0500

You could look at changing the thermal efficiency of your boiler supplying the hot water to the FCUs (I am assuming you are using water coils on the airloop supply side). Whatever fuel your boiler is using (propane, fuel oil, natural gas, or electricity), increasing the thermal efficiency should decrease the fuel expenditure (i.e. amount burned or kwh used) required for the same air conditioning performance.

I think you should adjust the model so that more of the energy is being consumed during the occupied hours than the unoccupied hours; that is more realistic. You mentioned a few measures that could work for that, like setpoint adjustments and HVAC controls. You could also add lighting controls to respond to the occupancy sensors.

You also might investigate changing the efficiency of your pumps to reduce power consumption to move the water.

edit flag offensive delete link more


Thank you ! The boiler I have unfortunately provides about 4-5 buildings in reality so in Openstudio I modeled it as Autosized due to the limited data I have.

To what degree can the efficiency measures be implemented practically ? For changing the efficiencies of the boiler and the pumps, does this mean in reality to buy a new boiler and new pumps with higher efficiency ? Or can we still retain the installed ones and do something with them ?

Do you have further thoughts on measures that can implemented more practically to this existing building ?

Ahmad gravatar image Ahmad  ( 2021-07-01 01:22:50 -0500 )edit

I would refer to a boiler or pump contractor for your question on replacement vs upgrade existing equipment. For thermal efficiency, you might just need to change the burner engineering rather than replace the whole boiler. Switching out light bulbs to LED over other types might also be a good idea, which you mentioned above.

sashadf1 gravatar image sashadf1  ( 2021-07-01 11:19:11 -0500 )edit

Thanks a lot ! All the lamps in the building are of LED type installed in 2016. Their details are in the link here:

What do you think can be modified for these lightings ?

Ahmad gravatar image Ahmad  ( 2021-07-02 12:14:18 -0500 )edit

Also last question, for the variable speed pumps I have defined in Openstudio for the water loops, which parameters do you recommend to alter in order to change the thermal efficiency ?

Ahmad gravatar image Ahmad  ( 2021-07-02 13:42:30 -0500 )edit

Thermal efficiency would be more for burners and boilers than pumps, and is different from pump efficiency.

To affect the pump efficiency (i.e. how much electricity the pump needs to draw to move H20) I would look at changing the motor efficiency (set to 1 if not already 1).

Also look at the Pump Design Power Consumption You may want to autosize or decrease it.

sashadf1 gravatar image sashadf1  ( 2021-07-02 19:09:47 -0500 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer


Question Tools

1 follower


Asked: 2021-06-30 13:00:41 -0500

Seen: 72 times

Last updated: Jun 30