Technical Paper presented at ACRECONF 2007, Delhi, Hourly Load Calculation Analysis Programme for Indian Cities

Tuesday, December 11, 2007

Hourly Load Calculation Analysis Programme for Indian Cities

Vikram Murthy and Rajeev Kakkar, ISHRAE Mumbai Chapter

Rajeev Kakkar is a Technical Consultant (HVAC) by profession, a graduate from I.I.T Kharagpur, and has over 30 years of experience in the field. He is also the webmaster for, the Technical advisor for the "Hourly Load Calculation Programme" sponsored by ISHRAE, and faculty for IIE, the "ISHRAE Institute Of Excellence" training programme series conducted by ISHRAE Mumbai Chapter.

Vikram Murthy graduated from IIT Kanpur in Electrical enginering in 1975 . He is Director of Univac Environment Systems Private Limited and Trustee of Tropical Airconditioning and Refrigeration Institute , a recognised Training Centre, for Technicians and Engineers. He has 33 years of diverse experience in leading HVAC Contracting Companies , is active professionally and socially , serving ISHRAE as the President of the Mumbai Chapter for 2007 - 2008 and The Rotary Club of Bombay Film City since 1992.


The ability to make sensible decisions regarding the HVAC design with respect to environment and economics is of utmost importance. Air-conditioning load calculations in India have been carried out using single day peak load manual calculations. The commercially available tools for load calculations are either too simple to be used for professional work (low-end packages) or too expensive with long and difficult learning curves. In a recently concluded research project, ISHRAE and ASHRAE India Chapter have developed a database of the hourly values of climatic parameters. The next step obviously was to develop an Hourly Load Calculation Programme.

Key words: hourly load calculation programme; HLCP; cooling loads; EnergyPlus; ECBC; building energy simulation; hourly weather data


Considering the fact that there is an urgent requirement of a validated HVAC sizing programme which uses BIS Design Day Standards and also provides hourly outputs using the heat balance equations found in EnergyPlus (and as adapted from BLAST), the development of HLCP as an ISHRAE project has been timely. The ability to make sensible and well-based decisions regarding not only the prediction of energy consumption in a building during the conceptual and design stage, but also to be able to finally size the HVAC system, both with respect to environment and economics, is of utmost importance.

Current Methodologies:

Currently, HVAC sizing loads is carried out mainly by manual and spreadsheet methods based on the de-facto standard of calculating instantaneous heat gains using methods developed by Carrier, and based on tabulated empirical ETDs (Effective Temperature Differences) for fenestration, walls and roofs, apart from a myriad of programmes developed by individuals, which have not really been validated. The current methodology also adopts use of design day weather data based on simultaneous peak occurrences of DB temperature and WB temperature, and whose validity and source is not known and has been lost in antiquity.

Weather Data:

In 1999 the Tata Energy Research Institute (TERI), developed a set of hourly Indian weather data sets for 52 stations from measured sequences of climatic data from 1981 to 1992 based on the concept of "coincident" temperatures in line with and in the format as published in the ASHRAE Handbook of Fundamentals, 1997. With the availability of WeDCo hourly and DesignDay weather data, and with the virtually simultaneous availability of a stable version of the EnergyPlus simulation engine, an opportunity arose to create a cooling load programme using WeDCo weather data as an input to EnergyPlus.

As EnergyPlus is more of a "black box" with a shell for input, which is more suitable for research rather than day-today sizing calculations, it was logical to propose and deliver a HVAC sizing programme with a GUI to serve the needs of the community in India.

Interfaces and tools:

The commercially available tools so far for energy analysis and load calculations were either too simple to be used for professional work (low-end packages) or too expensive with long and difficult learning curves (high-end packages).

HLCP, hourly Load Calculation Programme:

HLCP is simplified zone-by-zone method for calculation of HVAC cooling loads for sizing of equipment specifically for Commercial buildings, based only on numerical inputs. HLCP uses the "Purchased Air" system type in EnergyPlus which is itself implemented based on the ASHRAE cooling sizing method and the cooling design load calculations are carried out using the standard ASHRAE Heat Balance method. That solves the issue of validation. HLCP is not just a graphical user interface for the EnergyPlus simulation engine; rather, it's an interface to calculate hourly loads. Post-processing of the data also takes care of the hourly latent loads. The user interface has been kept free of icons, with tabs and buttons in plain English, so that even the average HVAC engineer is able to use HLCP after a few trail runs. The interface has been designed as a tabbed wizard, again for ease of use, without unnecessary clutter of providing options which may really not be relevant for an HVAC sizing exercise.

HLCP can do what manual or spreadsheet HVAC sizing programmes cannot. That puts HLCP right in the path of the ECBC. In all likelihood, energy simulation interfaces built over EnergyPlus, such as DesignBuilder will be prominently used for compliance with the ECB code, during the Feasibility and Site Planning phase, and the Outline Design Phase of the building. During this stage, it would be necessary for the building to comply with the ECB code, and at this stage the Architect would have a much greater say than the HVAC designer. As the building design moves to the Scheme Design and from there to the Detailed Design, it is the HVAC engineer who will most likely call the shots.


On 27th May 2007, The Bureau of Energy Efficiency, India, BEE, released the Energy Conservation Building Codes ECBC, for Commercial Buildings. One of the clauses in the ECBC (apart from the clauses which specify the U values for walls, roofs and fenestrations), is that "The equipment capacities for the standard design shall be sized proportionally to the capacities in the proposed design based on sizing runs; i.e., the ratio between the capacities used in the annual simulations and the capacities determined by the sizing runs shall be the same for both the proposed design and standard design. Unmet load hours for the proposed design shall not differ from unmet load hours for the standard design by more than 50 hours."


This really means that it would be a wise step to compare the energy simulation loads with the design loads in parallel, as the building design moves from the feasibility and site planning stage to the detailed design stage, so as to ensure that this requirement of the ECBC is met without any ambiguity. The use of a building energy simulation programme in conjunction with HLCP, using the same weather data and the same simulation engine, in this case, EnergyPlus, would ensure compliance.

Further Information on HLCP can be found at:


[1] ASHRAE Handbook of Fundamentals 1997

[2] Proceedings of the 23rd National Renewable Energy Convention, pp. 284-289,
edited by R L Sawhney, D Buddhi, and R P Gautam. Indore: Devi Ahilya

[3] Review of Inside Design Conditions in Air Conditioned Spaces, by N. S. Hukmani, The
Air Conditioning and Refrigeration Journal, January 2004.

[4] Weather Data & Design Conditions For India,
booklet published by ISHRAE and AIC

[5] InputOutputReference.pdf, 2007
EnergyPlus documentation.

[6] Carrier Systems Design Manual

[7] Weather data - ISHRAE

[8] EnergyPlus: The Merger of BLAST and DOE-2, 1998 - Dru Crawley

[9] What outside Design Conditions should I use in calculating a heat load?

[10] ECBC 2007


Post a Comment