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

[Brian Fountain]

This is a great question that has puzzled me in the past.

The difference between the hourly reports BUILDING-LOADS and BUILDING-HVAC is the same as the difference between the heating and cooling reported in the LS- reports (LS-C for peak and LS-F for total) and the heating and cooling reported in SS-D.

LS- reports and BUILDING-LOADS are determined after the LOADS module is run.  SS- reports and BUILDING-HVAC are determined after the SYSTEM/PLANT module is run.

You are correct that the biggest difference is generally caused by ventilation.  There are a number of other factors that move the SYSTEMS heating and cooling energy.

Reheat –  reheat is not accounted for in LOADS but comes into play in SYSTEMS.  With a VAV system and a low supply air temperature you will see an increase in heating energy between your LOADS and SYSTEMS reports even without ventilation.
Humidity control – while LOADS reports latent loads, SYSTEMS reports the system response including reduced supply air temperature and reheat.
Thermostat setpoints – SYSTEMS uses the zone thermostats whereas in LOADS the space temperature estimate is used to determine loads  for all hours.  This can have a significant impact on unconditioned spaces where the default SPACE temperature is 70F for LOADS but may vary considerably from this in the SYSTEMS module.

Mohamed provided a much more comprehensive list of the differences between the LOADS and SYSTEM runs – I am very curious about the source of that list?


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Brian Fountain
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From: Equest-users <equest-users-bounces at lists.onebuilding.org> On Behalf Of Konstantina Kalliakoudi via Equest-users
Sent: March 11, 2020 3:49 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Difference between "Building -Loads" and "Building -HAVC"

CAUTION: EXTERNAL SENDER
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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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