Software simulation

Energy modelling can be a valuable tool in MEP system design, but how do you select the best one to meet a specific project's needs? Ahmad Gabir gives a comparative analysis of the current options available.

ANALYSIS, MEP

Energy modelling can be a valuable tool in MEP system design, but how do you select the best one to meet a specific project's needs? Ahmad Gabir gives a comparative analysis of the current options available.

Energy simulation or modelling is indispensable for almost every project - especially during the early stages of the design. However, many engineering consultants rely on load calculation programmes that are supplied by equipment manufacturers and cannot integrate some of the complex architectural features into the overall building performance.

The growing demand for sustainable construction in the Middle East and the movement towards the use of the US Green Building Council's (US GBC) Leadership in Energy and Environmental Design (LEED) certification system have increased the trend to utilise simulation tools to analyse the energy performance of buildings.

The most three common questions that are posed today about energy modelling tools are:

  •  What is the best energy model software currently available?
  •  Does it meet the needs of LEED?
  •  Does it include real Middle East or, in particular, Dubai weather data?

LEED modelling

It is important to note that the LEED rating system doesn't limit designers to a specific software programme as long as the simulation tool has the capability of performing the following requirements of ASHRAE 90.1 2004:

  • A minimum capacity of 1,400 hours per year;

Hourly variations in occupancy; lighting power; miscellaneous equipment power; thermostat setpoints; and hvac system operation, that can be defined separately for each day of the week and holidays;

  • Thermal mass effects;
  • Ten or more thermal zones;
  • Part-load performance curves for mechanical equipment used in the system;
  • Capacity and efficiency correction curves for mechanical heating and cooling equipment;
  •  Air-side and water-side economisers with integrated control;
  • The budget building design characteristics.

Leed for New Construction (LEED NC) EAc 1: Optimise energy performance requires five energy simulation runs to satisfy the requirements of the whole building energy simulation. Four runs should be identical to enable a baseline design-model to be established, except for the building orientation and the minimum ASHRAE 90.1 requirements for the solar heat gain co-efficient. The fifth run will be used to assess the proposed building model.

Software selection

There have been may energy programmes and software systems developed during the last fifty years. The majority of the energy modelling software features an engine that accepts a simple text-based input. This engine contains thermodynamic algorithms that are used to calculate energy performance.

Such tools have been developed for use during the whole process of the building life cycle. They are capable of predicting the annual energy performance of the building. The software used in the building energy field is actually fully-fledged energy software and the importance of such programmes cannot be denied.

These types of software provide users with real-time information of building performance such as energy demand, temperature, operating costs and humidity. Some of the software programmes currently available are IES VE, Ecotect, HAP, Trace, eQUEST, EnergyPlus and PowerDomus (see box below).

It is quite difficult to select the ultimate software because it doesn't exist. Energy software selection depends on the designer's exact requirements, where the designer needs first to identify their energy analysis methodology. A few of these software solutions are quite expensive, costing around US $20,000/year (AED73,460) for example, but the majority are offered either for a reasonable price or free.

As for the weather data, the UAE still does not have measured solar data both for direct and indirect radiation, however Masdar initiated a field measurement process last year to gather such data. The UAE Airports also have weather stations with extensive records of temperature, relative humidity and wind data.

Most simulation programmes consider an hourly temperature profile for a sample day of each month and hypothetical averages with both dry bulb and wet bulb temperatures peaking at the same time, which does not reflect the real data. Although the resulting predicted annual energy simulation is within 20% of the actual field data, the demand peak cooling and electrical loads would be around 30% lower than the actual peaks recorded due to the use of averages.

It is important for the engineering community worldwide to design systems using accurate measurement tools and a proper automated reporting system.

These should generate reports that are based on hour-by-hour and month-by-month field data to enable the engineer to have a verification tool to check if their simulation is in line with field historic data. Some such field measurements that can be used as reference are available and well documented in the developed world and partly in UAE.

Available software for energy modelling of MEP systems

IES VE

IES VE offers professional designers a variety of ways by which to analyse design-oriented buildings in a convincing environment. It uses a three-dimensional (3D) geometric explanation of the building to which data is then attached in order to perform specific design tasks. One of the principal features of IES is the possibility of importing the REVIT model.

IES can be used to perform daylighting analysis and validate if the requirements of LEED EQ c8.1 Daylight and view will be met. It can also perform a computational fluid dynamic analysis and predict the percentage of occupants that would be dissatisfied with thermal comfort in the proposed building.

It is considered to be a dynamic simulation software tool that is based on the principles of the mathematical models of building energy transfer procedures. It offers a complete evaluation of systems and building designs and can also be used provide yearly building energy simulation models.

Ecotect

Ecotect is considered to be a whole environmental design software. It includes features for cost analysis, lighting, thermal, solar and interface for three-dimensional (3D) modelling. It can make efficiency analysis more accurate and easy.

The software is based on the idea that environmental design ideology is most successfully addressed throughout the conceptual process of design. The tool provides necessary analytical and visual advice from the simple drawing model to a more detailed model. It is capable of utilising shading models to complete scaled cityscapes.

Ecotect is suitable for use in coaching beginner designers, enabling them to design numerous significant concepts that are essential for competent building design. Broad assistance files and tutorials are also included and it has a 3D computer aided design (CAD) interface that allows support of the simplest drawing design to extremely compound 3D models.

It has the ability to import DXF and 3DS files. The programme also permits the user to test design ideas at the abstract phases by giving important examination advice such as whether the modelling geometry and data are being used in a wrong way or which data is the more important to the final design.

EnergyPlus

EnergyPlus is a modular tool that has been developed by combining the abilities of DOE-2 and BLAST. It is designed to predict the precise comfort and temperature in an integration simulation. It can be used to calculate the cooling, heating and electrical responses of a system.

The step-by-step solution provided by the software can give more precise temperature and electrical predictions. It is also important for analysing radiant, inter-zone airflow and moisture absorption.

Energy Plus has two parts: the building simulation module and the mass and heat balance module. Released in April 2001, it is currently widely used in research laboratories, universities for research, and in engineering firms. One of the weaknesses of Energy Plus is that the input text is sometimes more difficult to handle than graphical structures.

Equest

Equest is a user-friendly energy modelling tool that includes a creation wizard that is designed to form a building energy model. It includes several features and abilities to describe the design aspects and the impact of energy on it. It is suitable for designing area usage lighting systems, construction materials and hvac materials.

Initially it compiles a description of a building, then creates an overall building simulation. It can provide a wide range of graphical formats to view the simulation results. It can also be used to compare building energy on a monthly or annual basis. Equest enables users to carry out various simulations and presents results in a graphical format. It provides an implementation of energy efficiency and system control; the latest version also provides a 3D building geometry view.

HAP and Trace

HAP and, similarly, Trace provide an Explorer-like graphical user interface (GUI) that offers users rapid and well organised access to task data. In order to describe components of heating, ventilation and air conditioning (hvac) and building systems, a modular scheme is used. This approach eases the configuration of data to meet a broad range of applications.

HAP provides a system-based loom to devise calculations that modify sizing measures and inform the particular kind of system being designed. This presents efficiency compensations over easy load calculation programmes that require the engineer to produce calculation outcomes that are relevant to the range of components that are being used in the system.

Features of HAP are suitable for split systems, vertical units, rooftop units and central air handling units for example. It offers features for the rapid design of fan coil units and water source heat pump systems. Data is included for middle heating and cooling and boilers. It can provide reports in the form of psychometric charts, hourly loads and component load.

HAP is best suited for retro-fit and construction applications. The energy expenditure data and efficacy tempo information is used to compute the price for each energy resource or type. HAP can provide monthly, daily and hourly simulation results, which can be presented in graphical and tabular formats.

PowerDomus

PowerDomus enables the user to view the path of the sun and several shading effects. It provides graphical reports of capacity, daily moisture, temperature content and thermal loads etc. The on/off control techniques can be used on heaters with one minute time intervals. Conditions such as adiabatic and impermeable surfaces or the effects of moisture can also be visualised. In addition, the software offers a view of the distribution of moisture and temperature in soil according to a user-provided sample.

Ahmad Gabir is a senior electrical engineer with DC Pro Engineering and a LEED Accredited Professional (LEED AP).

 

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