Radiant Cooling and VRV systems giving Lower savings than anticipated in DesignBuilder

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Dear All,

Greetings. I am Kartikay Sharma, student for MTech Building Energy
Performance at CEPT University. I am Right now using Simulations as a tool
in my thesis to estimate the energy savings potential of buildings. For
this purpose, I am using DesignBuilder to simulate all ECM/EEMs.

Three of my selected ECMs are :

1. ECBC compliant chiller(centrifugal with 6.3 COP with VAV AHU and VAV
terminal units)
2. VRV systems
3. Radiant cooling

My base-case system uses a water cooled system with an screw chiller of 5.2
COP and Constant Air Volume (CAV) AHU. The problem that I am facing is
that, I am getting higher savings(overall EPI savings) if do ECM1 listed in
table, but looking at case studies the savings from ECM3 should be higher
than ECM1. Similarly I am facing problems with ECM2. The weather selected
for my building is Hot and Dry climate of Ahmedabad.

So I request all the members to help me in the same

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Bldg simulation's picture
Joined: 2016-04-13
Reputation: 400

Hi Kartikay,

I recommend you worth checking all the models thoroughly before arriving on
any conclusions. I quickly checked some of the critical parameters for
Radiant case and found some issues but not limited to as follows:

- The Radiant chiller is set-point manager is at OA reset and operate at
6 degC regime. In general, Radiant, TABS system works on raised chilled
water supply temperatures (14-15 degC) compared to conventional system
which is at 6-7 degC. Refer the EDR

resources to know more on this.
- The AHU (DOAS) has a coil size of 4.8 MWc and supply volume of 149
m3/sec (400,000 CFM) which means AHU takes most of the cooling load
compared to the radiant system. I believe, DOAS is in the design to meet
ventilation loads ONLY. Additionally, if this is to meet ventilation loads
and supplying air directly to the zones, the supply air set-point should be
very close to the zone set point temperature~21-22 degC. You should also
look into *equipment sequencing* in order to make sure each system is
meeting the desired loads (Radiant meeting sensible loads and DOAS all the
ventilation loads).
- Most importantly, DesignBuilder/EnergyPlus has great flexibility in
generating variables to do quality checks which is very useful and must
have before arriving on any preliminary conclusions. Remember garbage in,
garbage out...

Similarly, other model should be investigated accordingly.

Hope this helps!!

Bldg simulation's picture
Joined: 2016-04-13
Reputation: 400