Product(s):	OpenBuildings Energy Simulator
	Version(s):	CONNECT Edition
	Area:	Calculations

Overview

The following steady state calculations are available in OpenBuildings Energy Simulator:

 

Method

• ASHREA 90.1
  Assesses building compliance according to 2010, 2007 or 2004 requirements. Provides the minimum requirements for the energy efficient design of buildings except low-rise residential buildings. This includes all new buildings, additions and retrofits. Results given for Summary, Building Envelope, Lighting, Service Water Heating and HVAC.
  
  
• ASHRAE 62.1
  2010, 2007 and 2004 are all available. Used to specify the minimum ventilation rates and indoor air quality that will be acceptable to human occupants and are intended to minimize the potential for adverse health effects. The standard applies to new buildings, additions to existing buildings, and retrofits identified in the standard. The standard is intended to be used to guide the improvement of indoor air quality.
  
  
• PartL 2021 & 2013
  For assessing and producing building Compliance documentation and Energy Performance Certificates, using the SBEM calculation engine. England, Wales, Scotland and Jersey all available.
  
  
• Heat Loss

ASHRAE Heat Loss - Used to display results from the ASHRAE Heat Loss calculation in several report formats. Losses for individual room surfaces are detailed on the full report. Total losses for rooms can be viewed in the summary report. Results can also be viewed graphically on the Graph tab.

CIBSE Simple - Used to display results from the CIBSE heat loss calculation conducted using the Simple Model steady state heat loss model. The Simple Model assumes that the heat transfer coefficients can be lumped together and assumes rooms are cubic when considering radiative heat exchange. The mean radiant temperature is assumed to be the average of the internal surface temperatures. Other approximations are made to heat transfer processes, which enable all heat flows to be considered as being to the air point or the environmental point. The heat transfer relationship between these two points is then established for the room, enabling heat losses to be computed. 

CIBSE Basic - Used to display results from the CIBSE heat loss calculation conducted using the Basic Model steady state heat loss model. The Basic Model, also referred to as the complex model, involves carrying out a rigorous heat balance for the room, considering convective and radiative heat transfer separately. The complex heat loss model calculation results are often different from those obtained using the simple heat loss model. It is considered more accurate results because it is based on a more accurate analysis of room heat transfer, with fewer approximations. 

• ASHRAE RTS
  Used to display results from the ASHRAE RTS (Radiant Time Series) calculation. Hourly total loads are provided with breakdown of loads through fabric, glazing, infiltration, internal gains. Gain through each surface can be viewed. Total Peak Room loads can be viewed in the Summary report.
  
  
• CIBSE Heat Gain
  Calculates heat gains using the method described in Section A5 of CIBSE (UK) Guide. Peak room loads and a breakdown for Solar, Fabric, Convective, Latent and Casual loads are produced (info here), along with the resultant Air Flow Rates required to maintain your design temperatures in each room.
  
  
• CIBSE Maxi Gain
  This program finds the peak heat gain month for all included rooms and the coincident peak month for the group of rooms. Computes heat gains using the CIBSE method for each month to find the peak month.
  
  
• Summer
  Summertime temperatures in rooms are computed for your design day using the method described in CIBSE Guide Section A5. Hourly outside temperatures, time of peak, and peak internal temperatures are displayed.
  
  
• Air Flow
  Calculates the total air flow to all the rooms included, assuming either a constant volume or VAV system. Results are given for sensible and latent gains, together with the computed supply air temperature for each room. 

 
To examine the formulae and calculation methods behind each of the above, you can directly examine results as shown in this article.