[Bldg-sim] Diversity factors

Rathna Shree rathnashreep at yahoo.in
Tue Aug 12 23:09:10 PDT 2014

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?


On Tuesday, 12 August 2014 10:16 PM, Cheney <chenyu73 at gmail.com> wrote:

​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,
Connect with me and view my   http://lnkd.in/bqQf52i

On Aug 12, 2014 4:24 AM, "Bharath Seshadri" <s.bharath at ntu.edu.sg> wrote:

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
> 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 &  www3.ntu.edu.sg/erian/ 
>From:Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Rathna Shree
>Sent: Tuesday, August 12, 2014 5:51 PM
>To: bldg
>Subject: [Bldg-sim] Diversity factors
>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.
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