First time here? Check out the Help page!

Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question
4

Winter Designday heating load higher when I add drape to window

asked 6 years ago

updated 6 years ago

To see how a window shade will affect the zone load, I modified the EnergyPlus Example Exercise1D to add a drape to the two windows. (and modified the lighting power for winter designday to 0 watts).

When I compare the winter designday heating load for the bare window and draped window case. I found that the draped window case actually have higher heating load. See the attached picture.

While this seems somewhat counter intuitive, I tried to output all the surface temperature and convective heat transfer rate from EnergyPlus. From the results, what I can see is that for the bare window case, the convective heat transfer rate on all the surfaces added up to match the zone heating rate. But for the draped window case, the sum of all surface heat convective heat transfer rate is much lower than the zone heating load. Looking at the surface inside face temperature, I guess that the window surface temperature reported by EnergyPlus is the drape inside surface temperature. I am guessing that in calculating the zone heating load, EnergyPlus accounted for the drape outer surface and the bare window inner glass surface convection with the room air, but they are not reported in the surface convection heat transfer. My questions are:

  1. Is there a way to output the convection heat transfer rates on the outer surface of the drape and the inner surface of the bare window glass so that they add up to the zone heating rate?
  2. The result of window with drape having higher heating load still does not make sense to me, are there any settings I should change in my model to better represent the physics?

Here are the links to the two IDF files:

1. Bare Window

2. With Drape

image description

Preview: (hide)

1 Answer

Sort by » oldest newest most voted
1

answered 6 years ago

TNZ Energy's avatar

Did you look at the difference in solar heat gain in the space? Blocking radiant heat gain would certainly increase loads on the heating system.

Preview: (hide)
link

Comments

Thanks for your reply. The reported value is for winter design day. The sky clearness is set to 0, which means no solar radiation.

TiejunWu's avatar TiejunWu  ( 6 years ago )

Your Answer

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

Add Answer

Training Workshops

Careers

Question Tools

2 followers

Stats

Asked: 6 years ago

Seen: 296 times

Last updated: Jan 25 '19