[Equest-users] Thermal Blocks

[Jeremy Poling]

Jeff,
 
I too would be curious what the comment was verbatim, but I'm going to go out on a limb here and suggest something before that anyway.  I received a comment that I considered odd regarding how many systems were required.
 
ASHRAE 90.1-2007 clarified some requirements around system sizes, since there can be efficiencies from selecting more or less equipment for the baseline.  Section G3.1.1 was revised to require that baseline systems 1-4 be modeled with one system per thermal block and baseline systems 5-8 be modeled with one system per floor.  It does go on to allow grouping of floors with identical thermal blocks for modeling purposes.
 
This won't require a separate shell to model.  If your model is in Detailed mode right now, you'll need to re-assign zones to match.  If you somehow managed to keep the model in the Wizard mode (or for future models when you start out), you can select how eQuest assigns zones to systems (System per zone, system per floor, system per shell, or system per site).  For baseline 1-4 you would use system per zone and for baseline 5-8 you would use system per floor.  This is on screen 1 of the HVAC System Definition portion of the wizard.
 
I just checked with a basic, "default" model in the wizard, and eQuest will group floors onto the same system if you tell it to use floor multipliers and will create a separate system for each floor if you tell it not to.  I did a quick inspection of the reports (someone who knows more should correct me if I am wrong on this) and it looks like the floor multiplier can only be separated out by straight division, so you would want to make sure you can justify to the reviewer that you have identical thermal blocks for cases where they are combined but G3.1.1 says you should have separate systems.
 
Hope this helps - I made a big assumption, but hopefully this post will help someone else before they receive a comment back from a LEED review.
 
Jeremy R. Poling, PE, LEED AP+BDC

________________________________

From: equest-users-bounces at lists.onebuilding.org on behalf of Paul Diglio
Sent: Wed 5/4/2011 8:20 AM
To: Jeff Ross-Bain; equest-users
Subject: Re: [Equest-users] Thermal Blocks


Jeff:

ASHRAE 90.1 allow spaces of similar thermal characteristics to be combined in thermal blocks.  I do not include what you call support spaces because the load and occupancy is much different than, say a classroom.  I would define the corridor as a separate zone within the thermal block but served by the same HVAC system.  This allows you to have a different set-point, airflow, occupancy and schedules for the corridor.

You do not have to define a separate shell for each block, you can define the block by custom zones in the wizard.

I divide up a thermal block into as many reasonable zones as possible.  This allows me to find out which area of the thermal block is causing any unmet heating or cooling hours.  It also allows me to change the HVAC system control zone to that zone which is the hardest to satisfy in the summer and winter.  These zones can be served by a single HVAC system.

For a proposed model that needs to conform to an actual design, defining multiple zones per thermal block allows you to balance the airflow to zones that have unmet hours without increasing the overall airflow of the HVAC system.  I define the zonal airflow in the Zone tab.  I reduce the airflow to the zones without any unmet hours and increase the airflow to those zones that have unmet hours.  I do not define the total fan CFM in the Airside Systems tab.

What were the comments from the LEED reviewer?

Paul Diglio



________________________________

From: Jeff Ross-Bain <jeff at rbgb.com>
To: equest-users <equest-users at lists.onebuilding.org>
Sent: Wed, May 4, 2011 9:05:15 AM
Subject: [Equest-users] Thermal Blocks



Hi All,

 

Are there any additional discussions out there regarding thermal blocks besides what is in ASHRAE Standard 90.1 and the User's Guide? I have received comments back from a LEED reviewer that seems to reflect an interpretation of that concept which I have not seen before.

 

In a nutshell, does each thermal block require a separate shell with individual HVAC system? I understand the concept of having individual thermal blocks or combining these if they are similar space use categories. I am assuming then that the similar space use categories (say a college classroom building) can also include support spaces such as corridors, storage spaces, faculty offices, etc. 

 

So if several thermal blocks are combined into one, can they not be served by a single, similar type of HVAC system?

 

I hope that I have made myself clear and many thanks for your thoughts and comments.

 

Regards,

 

Jeffrey G Ross-Bain, PE, LEED AP, BEMP

404-228-2893 office 

404-408-2577 mobile
www.rbgb.com <http://www.rbgb.com/>