How to get peak cooling load and heating load of the ideal load system quickly?

Hi guys.
I am recently doing some different options for passive design. The energy modeling is done by Honeybee and OpenStudio. After runing some energy model,I am confused and a bit crazy for data analysis. I want to know peak cooling load and heating load of the ideal load system. Currently,I am using Honeybee_Normalize Data by Floor Area component for sum all zone cooling load and heating load.Then sort the list and find the max value. This workflow is so time-comsuming. Is there better way to get get peak cooling load and heating load? I want to analyze the load breakdown of the whole building. Is there better way to sum the output variable(people energy\lighting energy\solar gain energy etc) for all zone?

@minggangyin this is a little tangential from your question, but I believe there are some unnecessary steps/errors in your formula, from what I can read of your gh script. I assume you are trying to convert from kWh to kW (as it says in your panel output)?

In the second step you’re multiplying by 3,600,000 which I assume is 60 seconds x 60 minutes x 1000 (kilowatts to watt). I don’t think this is necessary:

  • If you’re trying to convert kWh to kW here, you just have to divide your total kWh (energy) by number of hours to get kW (power).
  • There’s no need to multiply by or divide by 60 x 60 that I can see because you’re already working in hours.
  • The output from the component is already kWh and you are converting to kW, so no need to multiply by 1000 b/c you are not converting to watts.
  • You multiply by 3.6x10^6 then divide by it later in the formula. That’s a sign you don’t actually need it in the first place!

Yeah,my current method is a little complicated.Thank you for you suggestions,I will follow it and improve my method.

@minggangyin ,

@SaeranVasanthakumar 's points are good but I will also add that engineers typically use a different method to size HVAC systems that does not involve an annual simulation like what you have run here. Because you are really only interested in the worst-case condition when you size an HVAC system, engineers will typically run the energy model through a detailed “design day” simulation or a day that mimics the wort-case conditions (using the data within the .ddy files). At the start of every EnergyPlus/Openstudio simulation with Honeybee, this design day calculation will be run to automatically size any HVAC equipment in the model. You can extract the result of this calculation using the “Honeybee_Read HVAC Sizing” component as you see in this example:
http://hydrashare.github.io/hydra/viewer?owner=chriswmackey&fork=hydra_2&id=Quantify_HVAC_Sizing_Impact_of_Shade

If you have a real HVAC in the model (not ideal air), this component will also tell you the actual size of the equipment, like the length of a chilled beam needed to meet the set point or the airflow that a fan coil unit must accommodate to meet the set point.

As for visualizations of the peak loads over the course of the design day, you can get this info out of the Honeybee simulation and it is helpful for understanding what is driving the resulting size of your HVAC. I have just pushed an example file that allows you to create these types of visualizations with Honeybee (and excel to make the nice-looking chart):
http://hydrashare.github.io/hydra/viewer?owner=chriswmackey&fork=hydra_2&id=Visualize_Peak_Loads_for_HVAC_Sizing&slide=1&scale=1&offset=0,0

There are a couple of important things to keep in mind when you use these visualizations:

  1. As you see in the example file, when you build these visualizations, you want to make sure that you are only looking at the sensible load in the space (not the latent) since it is ultimately the sensible heat that determines the size of the equipment needed to cool the space to the temperature set point. This isn’t to say that latent heat is not important but it primarily plays a role in sizing the ventilation system and not the equipment that heats/cools the space.

  2. The peak sum of the instantaneous loads in your chart visualization is typically going to be more than the result that you get from the “Honeybee_Read HVAC Sizing” component. The result from the “Honeybee_Read HVAC Sizing” component is actually what is being used to size the HVAC both in EnergyPlus and for an engineer. This difference is because the chart visualization is only showing you the heat instantly flowing into the space and does not account for the thermal mass of the space or the time lag between when heat enters the zone and eventually gets translated to sensible heat in the air. Once you account for this, your peak typically becomes a bit smaller.

I hope that helps!

3 Likes

3 posts were split to a new topic: Why analysis period doesn’t affect the HVAC sizing values?

@chris
Sorry to reply later.Thanks Chris!!!

Yeah,the Visualize Peak Loads for HVAC Sizing example file is pretty nice. It is just what I intended to do.

And for further analysis,I can extract the peak hour data and visualize the different load componts.
Here is an example.
Cooling load breakdown

That’s a cool idea with the pie chart, @minggangyin ! It seems like you are summing the loads over the whole design day, though, and I’m not sure what the purpose of that is.

I might recommend that you find the time in the day when the sum of all the loads is the greatest and use that time to make your pie chart. Then, you would be accurately showing the contributions from the different sources to the peak load and the size of the HVAC system. Solar will also be a much bigger component, then.

1 Like