Processing Energy Plus outputs. COP and?

energyplus
cop

#1

I’m about to present some data from my energy model and need to know if there are additional processes I need to perform similar to the COP calculations.

I have been wondering if my total heat load is accounting for internal gains through lighting, people, and equipment. Is this accounted for or do I need to subtract these units?

I also assume that my total heating and cooling is accounting for solar gain. I have tested this and believe it is.

Anything else I’m missing to get good numbers out?


#2

David,

I am not sure if I am understanding your question but energyplus is running an energy balance calculation that accounts for all of the terms that you see in this chart:

http://hydrashare.github.io/hydra/viewer?owner=chriswmackey&for…

If you are looking for output heating and cooling in units of electricity/fuel rather than heating/cooling load, I suggest that you run your modyl with a real HVAC system instead of the default ideal air loads as you see in this example file:

http://hydrashare.github.io/hydra/viewer?owner=chriswmackey&for…

This will likely be much more accurate than multiplying your ideal air loads by a COP.

-Chris


#3

Hi Chris,

COP depends on temperature e.g. in some building codes there are 2 minimum COPs required (T1,T3). What’s the accurate way in such cases? Would it make sense to make 2 groups of months or hours with average temperatures close to T1 and T3 and then divide each group’s energy loads by corresponding COP? Is there any way to calculate it fast and accurate?

Thank you


#4

@AryanShahabian ,
If you know what you are doing, rough calculations of the COP like what you mention can be decent ways of approximating energy use. However, the state of the art in energy modeling practice is to model fully detailed HVACs that use chiller objects in the energy simulation file. Such chiller objects are defined by curves (literally just polynomial equations), which calculate the COP as the simulation is running at every timestep of the calculation. They do this calculation using the outdoor air temperature, the temperature of the chilled water they are trying to make, the temperature of the water returning to the chiller, and the curve that you specify (which typically comes from manufacturer of HVAC equipment). Whenever you assign a system other than ideal air loads with the Honeybee_HVAC component, such chiller objects with default curves are being used. You can edit the coefficients of these curves within the OpenStudio GUI.

Let me know if that is clear.


#5

Thank you @chris for your comment.
Let’s say for instance we want to analyze the impact of glazing ratio on energy efficiency of buildings (in a certain climate e.g. Dubai), regardless of their mechanical/HVAC systems. In other words we want to look at the problem from an architectural point of view.

On the one hand, if we use ideal air loads, the results won’t include any COP, and on the other hand, if we set mechanical/HVAC systems, we should involve so many parameters and do multiple simulations which are far from the aim.

Please have a look at the attached image. It shows 3 pages of a green building code in Dubai, explaining the minimum requirements of HVAC systems.

According to your experience, do you think if there is any way to avoid modelling multiple HVAC systems while being able to reach results ranging close to reality?

Thanks


#6

Hi @AryanShahabian

I am not sure if I understood your question correctly, but if you wanna calculate zone thermal load without considering which HVAC system is used , you can obtain through the EIO file and the zone sizing output which relates to the building load which is only depending on your architectural design or passive strategies you used … and it doesnt take into account the mechanical system …


#7

@AMIRTABADKANI Thanks for your reply. Could you explain your method in detail? It would be great if you could share a simple example file.


#8

As depicted in the picture you can find calculated zone peak load and zone sizing value from the component below , the only difference between these two is that:
Zone Sizing = Zone Peak Load * Safety Factor

I hope this is what you were looking for …


#9

@AMIRTABADKANI
Thanks again, but the peak load doesn’t indicate annual thermal energy consumption. Does it?
I mean, maybe a system with greater peak load requires less energy during a whole year. Please correct me if I’m wrong.


#10

As far as I know, Zone sizing is used to calculate the HVAC system capacity and choosing the right system … therefore zone sizing or zone peak load is not about the energy consumption, but it is saying how much thermal load this unit has in Watts and what kind of HVAC system is a proper one to deliver the least energy consumption …


#11

I guess my question (this question: Processing Energy Plus outputs. COP and?) has been misunderstood a bit. Maybe I should ask it differently. But thank you for your reply @AMIRTABADKANI


#12

@AryanShahabian and @AMIRTABADKANI ,
It does seem like the two of you were referring to different types of studies. To answer your original question @AryanShahabian , I would just recommend that you be clear about your assumptions no matter what method you use. There’s far more complexity than simply multiplying by a COP between your ideal air demand and the actual full-HVAC energy use. In particular, such a multiplication method completely ignores the fact that you often need to cool down outdoor ventilation air to dehumidify it and then heat it back up a little before introducing it to a zone if the zone does not need cooling. So I would not refer to any post-processed ideal air loads as “electricity” or “fuel.” Just call them “cooling demand multiplied by COP” or something to that nature.

And I will also say that the application of HVAC templates in Honeybee is very quick. If you have to report values of electricity and fuel, you are likely better off using the defaults of these templates than trying to estimate electricity and fuel from a COP multiplication method.


#13

(This is also related to my previous question: https://discourse.ladybug.tools/t/what-is-the-most-efficient-hvac-system-for-tall-office-building-in-tropical-desert-climate/2846/2 )

Thank you @chris for your previous comments.

I would appreciate it if you could please have a look at the attached files (gh definition and epw file of Dubai). Question_AryanShahabian_01.rar (975.9 KB)

Could you please check the HVAC, thermostat and natural ventilation settings?

I have set a VAV+reheat. I’m not sure if I have set it correctly. Cooling results are high during winter. Is that because of relatively high humidity of outside air? or I have made a mistake?

These parameters are fixed and I cannot change them: construction of walls and windows as well as glazing ratio.

Other parameters could be altered (e.g. type of HVAC system, air details, heating/cooling details, thermostats, etc.). Current heating and cooling set-points are similar to reference models of climate zone 1-2 from https://www.energycodes.gov/development/commercial/prototype_models

I really appreciate any help you can provide


Any suggestion about setting old conventional HVAC system (for tall buildings in hot climates)?
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#14

@AryanShahabian ,
I don’t have time at the moment to check the file but I’ll say that the VAV w/ reheat HVAC system is notorious for having high amounts of cooling for dehumidification and then reheating it. (Hence, why the words “reheat” appear in the name). So that could explain why there’s still high cooling in winter. Other HVAC systems (like systems 11-17) do not have as much of this cooling down only to reheat but, as I said in the discussion you cite, these systems often involve coordination between architectural and engineering teams to pull off.


#15

Thank you @chris for your prompt reply. I’ll try systems 11-17. Could you please suggest some tutorials about setting all the HVAC systems listed in honeybee? It would help many people, who aren’t mechanical engineers, learn to use the tools correctly. LB+HB has made such processes much easier for architects and I think a good tutorial on HVAC would also be very helpful.