Dear All,
In most of the core and shell projects, the HVAC consultant would have considered diversity factor on the overall cooling tonnage. While modelling, we will be able to comfortably take diversity on occupancy, equipment and lighting loads. But diversity on fresh air cannot be taken. Because of which the project may end up with plant unmet hours. Please let me know how to tackle the issue.
Regards,
Rathnashree
Rathnashree,
1. Outdoor air minimum (code) amounts generally do not affect unmet load hours very much, so I don?t think you need to be concerned.
2. The HVAC system may reduce outdoor air amounts if it employs ?demand controlled ventilation?, e.g., CO2 sensors.
James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653
Hi Rathnashree,
Yes, it?s not easy for a core-and-shell building. We helped design a core-shell building recently. Here are some points we considered:
- What kind of tenants do you expect to occupy the space? Offices/Laboratories/Workshops etc?
- If its offices, you could take the same diversity as occupancy i.e. assuming you are using some kind of demand based ventilation control
- If its Labs/Workshops you could refer to design guides such as Labs21 or local standards
- But the best option would be to study metered data of buildings of the same function in your region to understand what an acceptable diversity factor for fresh air could be
Hope this helps. Do let me know if you need further references. Would be glad to help.
Regards, Bharath
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Bharath SESHADRI | Research Associate | Energy Research Institute | Nanyang Technological University, Clean Tech One, 1 Cleantech Loop, #06-09, Singapore 637141 (Map) | Mob: (65) 9321-9723 Tel: (65) 6592-3284 GMT+8h | Fax: (65) 6316-3195 | Email:s.bharath at ntu.edu.sg | Web: www.ntu.edu.sg
?
Well, I guess Rathna's question is the
?'?
conflict
?'?
between ASHARE 62.1 ventilation calc
? (100% OA systems)?
and
?OA
system sizing/design by designer:
for DOA or single zone ventilation calc, diversity factor shall not be
applied. However, taking school
? building?
as an example, HVAC system
?could be 'downs
ized
?'?
according to the diversified occupants
?when
designers believe the total number
? of students and teachers?
is fixed and they just move from one zone to the other.
?Bear in mind, ?
DCV
/CO2 control?
is
?the key which is ?
commonly used in order to
?accommodate
such "diversity"
?
.
?My understanding is that v
entilation calc
? without diversity?
in this case is actually calculating the maximum OA
? or sum of the diffuser flows?
for each room
?. From design point of view, two scenarios: 1. ventilation equipment can
be reduced with respect to such diversity factor provided CO2 control is in
the place. or 2. on the other hand, without CO2 control, conflict persists
and equipment sizing has to follow ASHRAE 62.1 calculation.
?Let me know your thoughts.
?
*Best Regards,*
*Cheney*
Connect with me and view my *http://lnkd.in/bqQf52i*
Hi Cheney/Bharath,
Thank you for the reply.
The fresh air is calculated and the system is sized as per ASHRAE 62.1 only.
I will elaborate the issue with an example. If the required cooling capacity after the heat load calculations is 1000 Tr, the diversity of around 80% will be considered for this 1000 Tr. The chillers are sized only for 800 Tr. In the simulation, this diversity considered by the designer will result in plant unmet. I tried reducing the plant unmet by reducing the occupancy, lighting and equipment loads by 20% in the schedules. But the 1000 Tr is calculated including the envelope and fresh air loads also. How to account the diversity from these loads?
Regards,
Rathnashree
?Well, I guess Rathna's question is the??'?conflict?'??between ASHARE 62.1 ventilation calc? (100% OA systems)??and??OA?system sizing/design by designer:
for DOA or single zone ventilation calc, diversity factor shall not be applied. However, taking school? building??as an example, HVAC system??could be 'downs ized?'??according to the diversified occupants??when ?designers believe the total number? of students and teachers??is fixed and they just move from one zone to the other.??Bear in mind, ?DCV/CO2 control??is??the key which is ?commonly used in order to??accommodate?such "diversity"?.?My understanding is that ventilation calc? without diversity??in this case is actually calculating the maximum OA? or sum of the diffuser flows??for each room?. From design point of view, two scenarios: 1. ventilation equipment can be reduced with respect to such diversity factor provided CO2 control is in the place. or 2. on the other hand, without CO2 control, conflict persists and equipment sizing has to follow ASHRAE 62.1 calculation. ? ?Let me know your
thoughts.??
Best Regards,
Cheney
Connect with me and view my???http://lnkd.in/bqQf52i
Hi Rathnashree,
Dear all, here are my comments and suggestions.
I use the following to determine a diversity in a building. From the simulation model the number of occupants based on say one person per 10m2 ( one per 100sf) is 800. Then look at the fire Marshall report for the number of people allowed in the building, also look at the elevator calculations to see on how many occupants the elevators have been calculated to and lastly if there is a cafeteria or canteen see how many people have been used in the calculations?
For simplicity let's say the fire rating is 600 occupants then the simple diversity is 600/800 =75%
Peter Simmonds, Ph.D., ASHRAE Fellow and DL
Mobile US: +1-310-383-9911
Mobile HKG: +852-9845-4902
Mobile UK: +44 7711 926317
FYI:
I think you?ll also find useful information in the ASHRAE Diversity Factor Toolkit ? RP1093 as well as the papers:
Claridge, D., Abushakra, B., Haberl, J. 2003. ?Electricity Diversity Profiles for Energy Simulation of Office Buildings (1093-RP),? ASHRAE Transactions-Research, Vol. 110, Pt. 1, pp. 365-377. ESL-PA-04-02-01 (February).
Abushakra, B., Haberl, J., Claridge, D. 2004. ?Overview of Literature on Diversity Factors and Schedules for Energy and Cooling Load Calculations (1093-RP),? ASHRAE Transactions-Research, Vol. 110, Pt. 1, pp. 164-176. ESL-PA-04-01-01 (January).
Jeff
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Jeff S. Haberl, Ph.D.,P.E.inactive,FASHRAE,FIBPSA,......jhaberl at tamu.edu
Professor........................................................................Office Ph: 979-845-6507
Department of Architecture............................................Lab Ph:979-845-6065
Energy Systems Laboratory...........................................FAX: 979-862-2457
Texas A&M University...................................................77843-3581
College Station, Texas, USA, 77843..............................URL:www.esl.tamu.edu
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Hi Rathna,
1. Load calculation usually takes the worst-case scenario. For cooling
peaks, all the internal loads, envelope and solar heat will be covered at
design temperature difference. In the real world, it is rare such worst
case will be predominant and it is not necessary to fine-tune every each
inputs of your annual energy model.
2. My understanding, as I mentioned in my last email, is that occupancy
diversity usually links with ventilation load and equipment rather than the
heat/cooling plant. Such diversity ?should compromise on building
envelope, etc. If the plant cannot handle envelope lost/gain, it is not
properly sized, period.
3. It is a common approach that a safety factor, say 15%, will be added
above the load calculation result for sizing the final cooling plant.
Unless I misunderstand your case, 80% downsizing the whole cooling plant
sounds abnormal to me especially nowadays load calculation software, such
as TRACE, has already considered block load and come up with a fairly
accurate results. ?
?Regards, ?
*Cheney*
Connect with me and view my *http://lnkd.in/bqQf52i*
A couple more references:
? The ASHRAE 90.1 User Manual has many typical diversity tables
? The Title 24 Non-residential Alternative Compliance Manual http://www.energy.ca.gov/title24/2005standards/nonresidential_acm/
? (I have attached a spreadsheet which contains those schedules from a recent version, but I?ve lost track of which version)
James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653