[Equest-users] Difference between "Building -Loads" and "Building -HAVC"

[Joe Huang]

This is an oft-repeated question, and an important one that I would like 
to elaborate.

DOE-2, the simulation engine behind eQUEST, simulates the building in steps.

In the first LOADS step, it calculates the heat flows in and out of each 
zone at a user-defined temperature (default is 70F). These heat flows 
are what appears in the eQUEST output as "Building loads".

In the second SYSTEMS step, it simulates the HVAC system and controls to 
derive the actual temperature of the zones, with the heating or cooling 
input by the HVAC system reported in the eQUEST output as  the Building 
- HVAC".

These two "loads" are very distinct.  In fact, I rarely look at the 
building loads except for debugging an input file.  Several things to 
remember:

1. The Building Load (BL) contains information for each building 
component (walls, roofs, lighting, infiltration, etc.) because those are 
all individual heat flow paths that are simply added together to get the 
BL for the space or building.

2. The Building - HVAC (BH) does not contain any of that because at this 
step DOE-2 is just using the total Space BL (SBL) in doing its 
simulation (note that in DOE-2 terminology,  it's called a "space" in 
Loads and a "zone" in Systems).  Furthermore, since DOE-2 derives the 
actual zone temperature in Systems, the SBL has to be adjusted, making 
it impossible to extract the component loads unless one does "reverse 
engineering" on the temperature difference, but would always be 
approximate due to thermal lag, thermostat deadband, etc.  (I can talk 
for days about extracting component-level loads from DOE-2 which I had 
to do for several DOE-2 projects back in the 1990s).

3. Natural or window ventilation is considered a Systems operation in 
DOE-2, so any effects from that will not appear in the BL, but only in 
the BH.

So, I hope that clarifies why the BL is always different from the BH!

Joe

Joe Huang

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
http://weather.whiteboxtechnologies.com  for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"

On 3/11/2020 12:49 AM, Konstantina Kalliakoudi via Equest-users wrote:
> image.png
>
> Dear equest users,
> I  generated  hourly report blocks looking for the loads.
> I saw that there are two options:
> 1. "Building Loads" which as far I understood contains losses, gains 
> etc....
> 2. "Building - HVAC" - Coils - losses&gains at te beginning I believed 
> that it cantrained : The Loads from the fresh air +  "Building Loads". 
> So in order to test that I made zero the fresh air at my AHUs. I was 
> expecting that now the "Building - HVAC" would be equal with "Building 
> Loads". But still there is a difference. "Building - HVAC" is higher 
> almost 50% than "Building Loads".
>
> Any Ideas or Comments about what "Building - HVAC" contains more than 
> "Building Loads"?
>
> Thank you for your help
>
> Konstantina Kalliakoudi
>
> Mechanical Engineer,M.Sc., LEED AP
>
> KHM
>
> Filolaou 28, Ilioupoli, Athens, Greece
>
> Tel. 0030 210 99 69 680
>
> www.khmoe.gr <http://www.khmoe.gr>
>
>
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