HVAC Cost and setEPZoneThresholds component

#1

Hi everybody !

I am writing you today to ask you some questions that I did not find somewhere else. Maybe this is obvious but there is something I do not understand.

I am trying to find the HVAC economy that I am doing with shading device. My problem is that I do not really understand the operation of the setEPZoneThresholds component.

1) What represent cooling set point/cooling set back and heating set point/heating setback ?

Lets see why I do not understand.
Here I put 17C for the heating set point and 27C for the cooling set point. However, after calculation inside temperature is still 28C (more than 27C, this is one of the reasons why I do not understand the setEPZoneThresholds component).


Then, to compare, I tried to take the cooling set point over 27C, namely 35C. Then my inside temperature is higher than the previous one, which is understandable because my set point is higher too.
Now an other problem, the mechanic ventilation energy increase, while the inside temperature is high and does not needs as HVAC as the previous example . It does not make sense.


Can you please explain me how this component works?

2) Is this way is the best way to know the economy of HVAC ?
I saw this other way about HVAC cost but numbers are totally different so I guess that it does not represent the same thing.


What is the difference between the mechanic ventilation energy and these values ?

Thank you in advance for your help.

#2

@Alexis ,

For future reference, it is usually better practice to split a post with two questions up into two separate posts (it helps others in the community search through the posts and benefit from the answers more). Still, to answer your questions:

  1. The cooling setpoint that you have there is working, as indicated by the fact that you get crazy high temperatures when you set it high and temperatures somewhat close to 27C when you have it applied. However, as the name “ideal air loads” suggests, the HVAC that you have in your model there is only keeping the air temperature of the room at the setpoint of 27C. Ultimately, the temperature that most occupants “feel” isn’t just a function of the room air temperature but also includes the effects of the surface temperatures all around the occupant (aka. the radiant temperature). When you have sun streaming through a window and falling onto the floor of a room, the temperature of the floor can get well above that of the room air, causing occupants to experience a radiant temperature much higher than the room air when they are closer to the window. The “operative temperature” that you are visualizing in that microclimate map is an average between the room air temperature and the radiant temperature. So that is why you see temperatures higher than the room air setpoint close to the window.

  2. Those numbers out of the readEio component are the correct ones that you should be using to evaluate the size/cost of the HVAC system. Specifically, those numbers represent the Watts that need to be added and removed from the entire space at the worst hour of the coldest darkest winter day and the hottest sunniest summer day respectively. This total number of watts is the sum of all the ways that heat leaves the space in winter (including envelope conduction, infiltration and mechanical ventilation) and all ways that heat enters the space in summer (including solar heat that comes through the window, heat released by people, lights, equipment, heat that comes in through the mechanical ventilation system etc). As you see, mechanical ventilation is only one of these terms so you won’t find any equivalence between the total size of the HVAC system and the energy that has to be added/removed from the ventilation air.

#3

Thanks for reply !

This is much clearer but now I have another question. I want to have the HVAC cost at all moment of the year, I do not want the maximum like the readEio component gives me.

Is it possible to find HVAC cost for each hours on a specific day ?

#4

@Alexis It is very easy to read every hour data of energyplus. You can use readEPresult component.