[Equest-users] Thermal Blocks

[Arpan Bakshi]

Jeff

Your query has generated a lot of discussion. Please attach the following
for your benefit--

1. Screenshot of your baseline equest zoning
2. Architectural floor plan



On Wed, May 4, 2011 at 6:26 PM, Jeremy Poling <
Jeremy.Poling at transwestern.net> wrote:

>  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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-- 

*
*
*

Arpan Bakshi  LEED AP BD+C
*
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