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Set points for shading control

asked 2015-02-11 08:38:17 -0500

AleMac gravatar image

updated 2015-07-11 13:14:04 -0500

In order to avoid overheating in the summer in office buildings, I would like to add a shading control that operates when solar radiation is above a defined set point (W/m2). However, this strategy would probably block welcome solar gains in the winter. Therefore I was thinking about a double shading control that takes into consideration also the outdoor air temperature. So, if outdoor air temperature > SetPoint1 & solar radiation > SetPoint2 then the shading device is lowered. Do you have an idea of typical values for SetPoint1 (°C) and SetPoint2 (W/m2)? I am working with EnergyPlus and Modelica, but I guess this is a general question. The building is located in Copenhagen (Denmark).

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I forgot to say that it is an office building.

AleMac gravatar imageAleMac ( 2015-02-11 09:02:50 -0500 )edit

Hi @AleMac - just to say you can edit your question to add more detail if you like.

Jamie Bull gravatar imageJamie Bull ( 2015-02-11 11:24:56 -0500 )edit
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@Jamie Bull -thanks, I have just added more details

AleMac gravatar imageAleMac ( 2015-02-11 14:52:17 -0500 )edit

I would think that this is dependent on location/climate class so you might want to add that to the question.

Jamie Bull gravatar imageJamie Bull ( 2015-02-11 15:18:31 -0500 )edit

location added to the question

AleMac gravatar imageAleMac ( 2015-02-11 16:13:44 -0500 )edit

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answered 2015-02-12 06:20:59 -0500

This is the perfect type of question to answer using parametric analysis since the answer will vary depending on many factors. Factors that will impact the setpoints include the orientation, the size and type of windows, the type and size of shading devices, if and how daylighting is used in the room, the specific location of the building, hours of operation, as well as the location and type of building. Because of this, even if you described all of these factors it is less likely that someone else will have tried the same control strategy and will be able to share a solution. Instead, you should use energy simulation to test a variety of values. Fortunately, I believe the two setpoints are relatively independent from one another so you can vary each one individually doing a series of simulations and it is likely that you will arrive at reasonable setpoints.

Here is the approach I would take. Start with the outdoor temperature setpoint. This may end up being close to the "balance point" of the building (the average temperature which is heating below and cooling above) since passive solar gains are really only beneficial to heating. First look through simulation results with no shading controls and see what the range of temperatures that the zones in the building need cooling instead of heating. Lets say that varies from 16C (61F) to 20C (68F). I would try simulations using just the temperature setpoint for controlling the shading devices of 14C, 16C, 18C, 20C, and 22C. Which ever of these simulations has the lowest enery use is probably the setpoint to use for temperature.

For the setpoint on the solar radiation (probably better called insolation) this is a tradeoff of view versus energy if no daylighting is used. For cloudy days, you still will end up with some solar radiation entering the room but the advantage of having no shading to the occupants is a larger view and perhaps more daylighting potential. You can do the same type of analysis using a variety of solar radiation setpoints looking at the impact on lighting energy (if daylighting controls are used) and on number of hours that shading is deployed. It might be more of a judgement. I would probably try a few different solar radiation setpoints (which vary depending on where they are being measured) from a fully overcast sky to a partly cloudy sky.

When you are done with this parametric analysis, maybe you have performed a dozen simulations but you will have setpoints that are optimized for your specific building. With this level of analysis, I would probably just modify the parameters by hand and keep a spreadsheet of the results to find the optimal value but if for more complex parametric analyses, you can use special tools to help such a JEPlus or EnergyPlus's Parametric objects or OpenStudio's PAT.

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Thanks for the exhaustive answer, Jason. Yes, parametric analysis would be an excellent method to find optimal shading controls in terms of energy vs. visual comfort. However, in my simulations, I am not considering daylighting and, at this stage of my work I am looking for very rough values. I think that the "balance point" you suggested for outdoor air temperature could be a good value. Regarding the insolation, maybe I could use a kind of average value of the warmest month (in this case is July).

AleMac gravatar imageAleMac ( 2015-02-12 07:34:16 -0500 )edit

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Asked: 2015-02-11 08:38:17 -0500

Seen: 281 times

Last updated: Feb 12 '15