The Multifamily Tool for Energy Audits (MulTEA) is an energy audit tool designed to provide auditors with an improved energy simulation tool for multifamily buildings and an improved tool for identifying cost-effective energy-efficiency retrofit measures for multifamily buildings. The unique construction, operation, and retrofit measures applicable to multifamily buildings require evaluating measures specifically for such buildings in order to obtain effective weatherization with high energy and dollar savings. MulTEA was developed jointly by the Oak Ridge National Laboratory and the Lawrence Berkeley National Laboratory. It was formally released within the US Department of Energy (DOE) Weatherization Assistance Program in 2017. MulTEA is included in the web-based Weatherization Assistant application.
MulTEA evaluates each building individually after taking into account local weather conditions, retrofit measure costs, and fuel costs, and specific construction and operation details of the building. MulTEA performs an hourly simulation of the building using the DOE-2 energy simulation engine in performing its calculations. After describing envelope components, heating and cooling systems, and base load equipment (e.g., refrigerators, water heaters, lighting), the energy consumption of the existing building can be estimated and calibrated to actual energy consumptions (i.e., utility bills). After an auditor defines and selects the retrofit measures to be analyzed, MulTEA produces a prioritized list of the weatherization measures for the building being evaluated. The output includes estimates of the energy savings, dollar savings, installation cost, and savings-to-investment ratio (SIR) for each recommended measure and the package of recommended measures to be installed. A method for determining the amount of leveraged funds needed to make the DOE Weatherization Assistance Program investment cost effective for each selected measure is also provided.
Implementation
MulTEA is implemented in four basic steps to select the energy efficiency measures for a particular building:
1. MulTEA guides the user through the process of entering data on a building that describe the characteristics of the building, its mechanical systems, and other energy-related information. The user also enters information on all the retrofits to be analyzed. MulTEA uses blower door measurements and steady-state efficiency measurements of space-heating and central water-heating equipment if available.
2. MulTEA performs a calibration run to estimate the existing (i.e., base case) energy consumption of the building and calibrate the building inputs using utility bills. MulTEA uses the DOE-2 hourly simulation program to estimate the annual heating and cooling loads of the building and the annual space-heating and space-cooling energy consumptions required to maintain the building at the specified thermostat settings. These calculations use weather data available from over 1000 cities in the US. They take into account solar energy absorbed by the building and the internal loads of the buildings from people, lighting, and appliances. MulTEA also estimates the energy consumptions associated with lighting, appliances, and domestic water heating by side calculations performed in parallel with the DOE-2 calculations. Currently the calibration is performed by comparing energy consumptions estimated by MulTEA based on standard weather conditions to energy consumptions based on utility bills that occurred for specific weather conditions. In the future, MulTEA will have the capability of performing calibrations using the same weather that the utility bills are based on.
3. MulTEA performs a measures run to evaluate the energy savings and cost effectiveness of individual energy efficiency retrofit measures applied to the building individually. In this run, each measure selected by the user is analyzed as if it is the only measure applied to the building, so there are no interactive effects between measures. This run provides the auditor with information to help in the selection of the measures to be included in the final package. MulTEA provides the capability of analyzing 36 different building envelope, space-heating and space-cooling, and baseload retrofit measures. Once MulTEA has estimated the energy savings associated with each of the selected retrofit measures, the user can enter the installation costs of the measures manually or using data bases that they have created to automate the process. MulTEA then calculates a discounted SIR for each measure using the estimated energy savings, installation costs, user-specified fuel costs, and measure lifetimes appropriate for each measure.
4. Finally, MulTEA performs a package run to evaluate the energy savings and cost effectiveness of a package of energy efficiency retrofit measures selected by the user for the building. In this run, the interactive effects between measures are accounted for. Beginning with the measure with the highest SIR, MulTEA applies each selected measure to the building and then recalculates a new SIR for the measure until all of the selected measures have been applied to the building. Repair and health and safety measures can be added to the package of energy efficiency retrofit measures selected for the building. Cost sharing/leveraging can also be specified and their impact on SIRs as viewed for the perspective of the weatherization program can be determined.