Re: [EnergyPlus_Support] Re: Design Day V.S. Schedule

On Thu, Jul 14, 2011 at 1:40 PM, YuanLu Li <yli006@xxxxxxxxxxx> wrote:

Zone 6 is facing South.

Earth tilt, latitude and roof tilt together may still an angle intensity reduction for that skylight on a Summer day.

I only did a sizing DesignDay simulatin, and should have max values in the sizing table.

Zone window heat gain includes all windows, and is not the beam transmission value through one sky light.

So you may be comparing different numbers. Your window names are all mixed, so I do not know which is which. The OpenStudio could not give me the window ID's.

In the HTML report summary choose Jtokwh instead of IP would give you the results in metric format.

Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: zqianmin@xxxxxxxxx
Date: Thu, 14 Jul 2011 12:03:43 -0700

Subject: Re: [EnergyPlus_Support] Re: Design Day V.S. Schedule

Dr. Li,

Thanks a lot. These additional objects come from openstudio template... I'll read your results carefully.

From my result variable, ZONE 6:Zone Window Heat Gain[W](Hourly) is 2959.68 at 07/31 13:00:00, which match the value of my hand calculation.

But, just in result table(html), WINDOW HEAT GAIN [Btu/h] max is 1380.75 for one skylight of 26ft2, which is about 1/3 of my hand calculation
zone 6 has two skylight,

I'm working on unit conversion now, and will run a simulation without unit conversion to check the number.

Regards,
Qianmin

On Thu, Jul 14, 2011 at 11:24 AM, YuanLu Li <yli006@xxxxxxxxxxx> wrote:

You have 500 unused material and constructions in your IDF. The attached IDF has been sorted and report variables added and deleted.

See whether the result in the csv files are reasonable.

Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: zqianmin@xxxxxxxxx

Date: Thu, 14 Jul 2011 10:08:48 -0700

Subject: Re: [EnergyPlus_Support] Re: Design Day V.S. Schedule

I choose " Run simulation for weather file run periods"

Here is the equation used to calculated window solar incident:

window_transmitted_hg = tau_D * E_D + tau_diff * E_diff

tau_D is the transmittance of the window to direct (beam) radiation
E_D is the incident direct (beam) radiation flux
tau_diff is the transmittance of the window to diffuse radiation
E_diff is the incident diffuse radiation flux

From my calculation @ 20:00
surface azimuth angle: 0
latitude: 38.7
declination: 20.64
solar time: 36

tilt: 18.97
incidence angle: 1.588(rad)
cos(incidence angle): 0.9998
SC: 0.64
transmittance of the window to direct radiation: 0.557

transmittance of the window to diffuse radiation: 0.511
incident direct (beam) radiation flux: 284 Btu/hr-sq.ft
incident diffuse (beam) radiation flux: 39 Btu/hr-sq.ft

transmitted heat gain=0.557 x 284.97 + 0.511 x 39.94 = 179.17 Btu/hr-sq.ft (565 watt/meter square)
window with 26sq.ft = 26 x 179= 4658 Btu/hr

1 Btu/hr·ft2 = 3.154W/m2

Above are my hand calculation

I'm not sure how energyplus calculate incident solar irradiance on window. Attached is my idf file.

I really appreciate your time, thanks.

Qianmin

On Thu, Jul 14, 2011 at 5:08 AM, YuanLu Li <yli006@xxxxxxxxxxx> wrote:

Cannot comment without knowing what is included in your hand calculation, and whether you were using DesignDay sizing or weather file run.   What is the listed solar direct normal value and Global diffused horizontal value used. What solar altutude angle did you use?

The location and roof tilt do not cover all the necessary conditions. You need to calculate the angle between the skilight normal and the solar beam at the time of calculation.

The maximum solar radiation intensity must not exceed 1400 watt/meter square. It is only around 1000 watt/meter square measured in Kuching, East Malaysia.

Because you are using IP units, it is not easy to compare the result with the weather file input conditions.

Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx

From: zqianmin@xxxxxxxxx
Date: Wed, 13 Jul 2011 14:41:00 -0700
Subject: Re: [EnergyPlus_Support] Re: Design Day V.S. Schedule

I have a skylight in my modeling, the simulation result shows this skylight has following maximum value
window transmitted solar of 1142.11Btu/h,
window transmitted beam solar of 858Btu/h
window transmitted diffuse solar of 284btu/h

window heat gain of 1382.65btu/h

this skylight window has a
u-factor of 0.35,
SHGC of 0.55,
Visible transmittance of 0.71,
23ft^2,
latitude of 38.7

longitude of -121.6 (Sacramental CA)
tilt angle is 18.97degree

hand calculating with radiant time series method give me following results:
window transmitted heat gains of 3360btu/h, which two times bigger than energyplus result.

I looked at the engineering reference, but still don't know why the value from energyplus are so small, about one third of hand calculating results.

Any one could give me some help? Thanks a lot.

Qianmin