[Bldg-sim] Thermal Blocks in Multifamily Residential Buildings

Mon Oct 26 10:52:03 PDT 2015

My strongest advice:  Good reviewers do not consider themselves
“un-convincible” but some effectively are when your own time/ability
constraints come into play.  Weigh your interactions so far with this
individual, and decide if you are better off “biting the bullet” and just
doing what’s been asked, as in such a case any discussions on this list
won’t change your situation and will only lose you time.

That said…

I expect your simplification to one block per unit is **probably**
appropriate, based on my general experience with multifamily projects of
varying types.  I’m the sort of personality that tends to err on the side
of “too much detail,” and I have constructed residential simulations
similar to what your reviewer is prescribing to find the added complexity
did not ultimately contribute to my confidence in the results.

Your reviewer is not incorrect however to point out that the actual design,
in reality, does have multiple thermostats and in a literal sense has more
than one zone per apartment unit.  Your reviewer and your project are in a
grey area.  Take note Sections 7 and 9 are not mutually exclusive: Section
9 prescribes “at least” one zone per multifamily unit in the same sentence
that allows for combining all units with a common perimeter orientation to
be combined.  I wish I could tell you 90.1 is clear as day on this front
and that Section 9 “trumps” Section 7 for multifamily, but I don’t think I
can make that case for a reviewer who is convinced otherwise.

Whether the reviewer is “right” or “reasonable” to suggest you break apart
the zones and distinguish the occupancy schedules (independent of what 90.1
says) is too context-dependent a question for anyone to answer absolutely
over this mailing list (and is ultimately a subjective question anyway),
though Julien is asking the right questions to provide an informed
opinion.  That you have a multi-zone arrangement in the actual design
suggests somebody felt it would at least improve comfort (not necessarily
save energy), which in turn suggests you’ve some expected substantial
variance in perimeter vs. core loads, *possibly* internal loads as well.
Whether such skin load variances and/or occupant-borne heat scheduling
should have a meaningful impact on system energy consumption is going to
depend on the system(s) itself, the occupant density we’re talking about,
and perhaps especially just how easily heat propagates between the zones
(which drives questions like “how big ARE these apartments?”).

Assuming the reviewer’s directives would take much more time for the full
project and you still have a degree of uncertainty yourself, I’d suggest
performing a ‘sensitivity study’ on a single apartment unit for your own
benefit (and perhaps to ultimately present to the reviewer).  Run the
simulation once as you have approximated the combining the actual
zones/systems, then again with the prescribed level of detail to match
actual zoning, as though you were following the guidance in Table G3.1
section 7. You can still freely combine zones with common “living” vs.
“sleeping” designations, as requested.  Ensure you have realistic degrees
of inter-zonal thermal transfer for that case.  Also be aware this is a
“rabbit hole” problem that can easily be overdone and unnecessarily eat up
your time – so don’t feel obligated to go the sidewalk’s edge.  Just test
the degree of detail requested by the reviewer and no more.

Critique the results for each run, consider/approximate the “scaled up”
impact of the difference in results for the project as a whole, and see if
you can demonstrate/convince yourself that ultimately this is not a big
deal by quantifying the potential swing in the overall numbers.

If this is something you feel motivated to try, I would advise first
starting a fresh conversation with your reviewer to propose this
sensitivity study/exercise (provide context:  explain the time-commitments
involved).  If you sense they are not going to accept anything more than
the detail prescribed for the full simulation effort, consider it time
saved and just “bite the bullet” per my initial advice!

Regards,

~Nick

*NICK CATON, P.E.*
*Owner*

*Caton Energy Consulting*
  306 N Ferrel

  Olathe, KS  66061

  office:  785.410.3317

www.catonenergy.com

*From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf
Of *Julien Marrec
*Sent:* Monday, October 26, 2015 2:25 AM
*To:* Sherif Farag
*Cc:* bldg-sim at lists.onebuilding.org
*Subject:* Re: [Bldg-sim] Thermal Blocks in Multifamily Residential
Buildings

Sherif,

Is it a local incentive program or your national energy code or something?

I don't know quite yet how to convince this person, but if you could give
us a few pointers about your project it may help.

Can you describe the HVAC system very briefly? What's your heating and
cooling system and how is it controlled? And do the residents have fully
manual control over the temperature? Do the residents pay for the utility
bills?

Also, how big are your apartments?

Julien

Envoyé de mon iPhone

Le 26 oct. 2015 à 07:31, Sherif Farag <sherif.sabr at gmail.com> a écrit :

Hi Julien,

No, it is not a LEED project;

I tried to convince the assessor but with no success, any advice? basically
he doesn’t agree with my interoperation and wants to see a clear document.

appreciate your help.

Thanks & Regards;

Sherif

On Oct 26, 2015, at 2:06 AM, Julien Marrec <julien.marrec at gmail.com> wrote:

Is this a LEED project?

Long story short, no I don't think this is a reasonable comment.

One block per apartment is common practice, and you can merge block if
their share a similar orientation.

Julien

Envoyé de mon iPhone

Le 25 oct. 2015 à 13:01, Sherif Farag <sherif.sabr at gmail.com> a écrit :

Dear Modellers;

I am modelled a multifamily residential building with thermal blocks
following ASHRAE 90.1:2007 Table G3.1 *item 9*. but I received a comment
from the reviewer asking me to follow Table G3.1 *item 7a* and justified
the comment because the living areas and bedroom areas having different
occupancy profiles, he also suggested that (to simplify the profiles) the
occupants are in the living space from 1800hrs to 2400hrs and in the
bedroom spaces 0000hrs to 0800hrs.

Is this a reasonable comment?

Did anybody here had a similar experience?

I will appreciate your feedback & recommendations.

Thanks & Regards;

*Sherif Farag*

*Sustainability Consultant*

P.O. Box: 127842

Abu Dhabi, UAE

M: +971 55 199 0022 | E: sherif.sabr at gmail.com | Skype ID: sherif.farag9

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