[Equest-users] Thermal Blocks

[Paul Diglio]

Jeremy:

Good explanation, thank you.

I model per the 90.1 zone definition.  If a zone is too large one thermostat 
cannot control it and we get unmet hours.  I zone the building for modeling the 
same way it would be zoned for airflow or VAV terminals, if specified.  I find 
that I can provide a better model if I create many zones and combine them.  This 
way I can adjust the airflow to each zone, choose the control zone, vary the 
ventilation air, change the set-point and schedule all while using just one HVAC 
system to feed all the zones as in a typical design.

I don't use thermal blocks too much, just for a situation like I mentioned in my 
previous e-mail, such as elevator lobbies on different floors served by the same 
HVAC system.  I do not understand the logic behind using large thermal blocks if 
the proposed design does not incorporate the same zone/block pattern.  I have 
reviewed models where the simulator created a thermal block consisting of an 
entire floor with glazing in three or four orientations, which does not comply 
with the 90.1 Appendix G requirements that zones in a thermal block adjacent to 
glazed exterior walls face the same orientation or the orientations vary by less 
than 45 degrees.

Paul Diglio




________________________________
From: Jeremy Poling <Jeremy.Poling at transwestern.net>
To: Paul Diglio <paul.diglio at sbcglobal.net>; Jeff Ross-Bain <jeff at rbgb.com>; 
equest-users at lists.onebuilding.org
Sent: Wed, May 4, 2011 6:26:03 PM
Subject: RE: [Equest-users] Thermal Blocks


Maybe this helps the definition debate (apologies for the length, but some 
things require more words to described).  Section 2 in ASHRAE 90.1-2007 gives 
the following definitions:
 
Space: an enclosed space within a building. (It goes on to define the different 
types of spaces, conditioned, semi-heated, etc., but those don't seem to be of 
concern for this discussion).
 
Zone: a space or group of spaces within a building with heating and cooling 
requirements that are sufficiently similar so that desired conditions (e.g. 
temperature) can be maintained throughout using a single sensor (e.g., 
thermostat or temperature sensor).
 
Thermal Block: a collection of one or more HVAC zones grouped together for 
simulation purposes.  Spaces need not be contiguous to be combined within a 
single thermal block.
 
Appendix G goes on to set up rules as to how to determine a thermal block in 
Table G3.1(7):
 
Where HVAC zones are defined on HVAC design drawings, each HVAC zone shall be 
modeled as a separate thermal block.  Exception: Different HVAC zones may be 
combined to create a single thermal block or identical thermal blocks to which 
multipliers are applied, provided that all of the following conditions are met:
a. The space use classification is the same throughout the thermal block.
b. All HCAV zones in the thermal block that are adjacent to glazed exterior 
walls face the same orientation or their orientations vary by less than 45 
degrees.
c. All of the zones are served by the same HVAC system or by the same kind of 
HVAC system.
 
 
The Users Manual has additional explanation on how to put together thermal 
blocks.  For the purposes of the LEED reviewers comment, don't forget that they 
are not assessing your use of the software you chose for the model, they are 
assessing whether you complied with Appendix G correctly.  The specific comment 
issued is related to G3.1.1 of ASHRAE 90.1-2007 specifically.  I couldn't tell 
from the screen capture if this was the case, but based on the comment I would 
assume that the reviewer agrees with you that your baseline system is one of the 
systems numbered 1-4.  They are expecting to see a separate system modeled per 
thermal block.
 
To address eQuest definitions, the DOE-2.2 Volume 2: Definitions classifies the 
"SPACE" keyword as an Envelope Component and more specifically, something 
the LOADS portion of the software uses to determine the loads to impose on a 
system.  the "ZONE" keyword is defined as an HVAC Component used by the HVAC 
portion of the software to determine the system and plant operating responses to 
loads in the building.  Very specifically, the ZONE keyword definition states:
 
"Each zone is associated with one and only one SYSTEM command, which specifies 
the system to which the zone belongs. This applies to conditioned zones as well 
as unconditioned zones and plenum zones. Note that there must be a one-to-one 
match-up between the zones specified here and the spaces specified in the LOADS 
program. That is, for each SPACE command in LOADS there will be a corresponding 
ZONE command to represent a physically identical portion of the building."

So you can see from the definitions in eQuest and in ASHRAE 90.1-2007 that the 
software is really not concerned with how many spaces are in a zone.  It relies 
on the modeler and HVAC designer to ensure that they have appropriately zoned 
the building.
 
In addition, I wouldn't interpret the reviewers comment as questioning your 
zoning at all: they specifically are asking that the model include 1 system per 
thermal block.  Unless you are using the exception (and it is an exception) that 
allows multiple zones to be combined into the same thermal block, this means 
that you will have one eQuest zone per system.  

 
For my personal interpretation: all of the wording in ASHRAE 90.1-2007 in G3.1.1 
and Table G3.1 really points to systems 1-4 being single-zone systems and 
systems 5-8 being multi-zone systems.  If you have a building that is 
non-residential, 3 floors or less, and less than 25,000 SF in real life, it 
would seem more probable that this building has single-zone systems and that 
larger buildings have multi-zone systems.  The system-per-floor requirement 
seems to match my experience as to how most mid-rise and high-rise office 
buildings are designed: one air handling unit per floor serving a primary duct 
system that terminal units in the tenant space connect to. 

 
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 4:46 PM
To: Jeff Ross-Bain; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Thermal Blocks


Jeff:

I've seen some of the other e-mails from the forum and I do not agree with the 
terminology other people are using, i.e. space v. zone v. thermal block.  Some 
of these replies are exceedingly long and contradictory.

Let's leave 'thermal block' out of the discussion.   Take one floor of an office 
building.  The baseline would usually require one HVAC unit for this floor per 
90.1.  I would create zones in the wizard for each large office space, the 
restroom, the utility rooms, the corridor and elevator lobby.  I would use the 
same procedure that you used below to add these zones to the HVAC system.  
Having the separate zones allows you to adjust the airflow and temperatures to 
the individual zones and also to find out where unmet hours might be occurring.

As an example of my understanding of a thermal block, say the office building 
has 8 floors and each elevator lobby is supplied by the same common HVAC 
system.  I would zone each lobby as described above and add them to the elevator 
lobby HVAC system.  This is a thermal block because it is a collection of spaces 
that share the same system and space characteristics.

Paul Diglio






________________________________
 From: Jeff Ross-Bain <jeff at rbgb.com>
To: Paul Diglio <paul.diglio at sbcglobal.net>
Sent: Wed, May 4, 2011 9:39:19 AM
Subject: RE: [Equest-users] Thermal Blocks

 
Hi Paul,
So you establish individual zones in the building footprint window (2) and 
discriminate between corridors, classrooms… but what about all the little 
closets, odd offices here and there, rest rooms, mechanical rooms, meeting 
rooms, etc.? It seems that the zoning patterns would then become a nightmare. In 
your Zone Group Definitions window (14) you would then assign the same system to 
each of those zones? Here is a screen shot of a zoning pattern. I have used this 
approach for years:
 
 
 
 
Jeffrey G Ross-Bain, PE, LEED AP, BEMP
404-228-2893 office 
404-408-2577 mobile
www.rbgb.com

________________________________
 
From:Paul Diglio [mailto:paul.diglio at sbcglobal.net] 
Sent: Wednesday, May 04, 2011 9:21 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
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