# Re: [EnergyPlus_Support] Re: Identifying the cooling energy use of individual zones

Hi Annie,

Just a minor update of the code to prevent "dividing by zero" error (which doesn't occur in your example but can happen under certain circumstances). Comments are in the file.

Cheers,
Ivan

Dr Ivan Korolija
IESD, De Montfort University, Leicester, UK

From: annie marston <anniemarston@xxxxxxxxxxx>
To: "EnergyPlus_Support@xxxxxxxxxxxxxxx" <energyplus_support@xxxxxxxxxxxxxxx>
Sent: Friday, May 17, 2013 8:01 PM
Subject: RE: [EnergyPlus_Support] Re: Identifying the cooling energy use of individual zones

Wow thanks Ivan, that is brilliant! Thanks. I will take a good look at the EMS this looks like a great solution. Gosh the knowledge and helpfulness of this help group continues to amaze me, thanks again.

Annie

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: ivankorolija@xxxxxxxxx
Date: Fri, 17 May 2013 10:30:01 -0700
Subject: Re: [EnergyPlus_Support] Re: Identifying the cooling energy use of individual zones

Hi Annie

I like Jean's approach. I spend some time today exploring the file you uploaded. The HVAC system has 4 chilled water branches (AHU's Cooling Coil loop + 3 chilled ceiling elements in B1Office, B1Office2 and B2Caffe) and bypass. Air is distributed to all thermal zones from the central AHU.

The question you would like to answer is how much chiller's electricity is consumed by Building 1 (B1Office + B1Office2) and by Building 2 (B2Cafe).

These are proposed steps:
1. Calculate fractions of the mass flow rate for each of 4 chilled water branches (note that the branch flow rate is divided with the pump flow rate decreased by bypass flow rate). This is used to calculate the portion of chilled water pump energy dissipated into each of the chilled water streams (energy which needs to be removed by the chiller as well).
2. Determine the chiller load from individual cooling elements (there are 4 cooling elements: cooling coil and 3 chilled ceiling elements). Equation looks like (cooling coil is in example): Q_CC_ChLoad = MassFlowRate_CC * cp * (T_CC_out - T_CC_in) * TimeInterval[sec] + CC_MassFlowRateFraction * CHL_Pump_HeatGain
Second part of the equation is to add pump dissipated heat to the water stream.
3. Calculate fractions of the air flow rates for each of 3 thermal zones (Air Terminal Flow Rate / AHU Flow Rate).
4. Determine the chiller load from individual thermal zones. For example: B1Office_ChLoad = B1Office_ChilledCeiling chiller load (calculated in the step 2) + B1Office_Air_FlowFraction * CoolingCoil chiller load.
Second part of the equation assigns the portion of cooling coil cooling energy (used to treat the air distributed to the thermal zone).
5. Knowing the chiller load from individual thermal zones and the chiller COP we can calculate the chiller electricity consumption. At the end, we just need to sum particular zones to get the chiller electricity consumption of individual buildings.

These steps can be done either in excel (post processing) or within EnergyPlus using EMS. I had some free time so I tried to encode this in EnergyPlus and the results are promising. HTML file reports chiller electricity consumption of 985.75 kWh, while I get 586.2 kWh for building 1 and 399.37 kWh for building 2 (985.56 kWh in total).

You can see the EMS objects at the end of attached file.

Cheers,
Ivan

Dr Ivan Korolija
IESD, De Montfort University, Leicester, UK

From: Jean marais <jeannieboef@xxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Wednesday, May 15, 2013 6:18 AM
Subject: [EnergyPlus_Support] Re: Identifying the cooling energy use of individual zones

Without thinking about e+, I would do it this way:
1) record the electric energy consumption of the chiller
2) record the VL and RL temps and mass flows at the pipe going to building 1 and at the pipe going to building 2
With massflow and dT, I can calculate energy out to building 1, building 2, and total. I can thus proportion the electricity usage at the chiller to building 1 and building 2.

In e+, I can also monitor these nodes (at each timestep) as above (chech the rdd file for the variable names to report...if you don't have an rdd file, then you still need to add the output request in your idf...it was something like Output:Variable,Dictionary,idf; but I don't know it by heart, so check the ioRef.).

Post processing in excell should be easy then.

Is this right?

Jean

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