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Description: Latest update of this popular software which provides an effective means of estimating heating and cooling system capacities for single-family concrete homes. Originally created as part of a HUD-sponsored project, this program accounts for thermal mass benefits not recognized in traditional residential HVAC design standards. The software calculates the system capacities based on the house dimensions, construction materials, air infiltration, location (U.S., Canada, and Mexico) and thermostat set point. Based on DOE 2.1E. Updated to latest ASHRAE Standards. MS Excel version 97 or later required for operation of the program.
This program uses a different approach than other HVAC sizing methodologies, such as Manual J and the ASHRAE Load Calculation Method. The Manual J and ASHRAE sizing methodologies were developed for low-mass frame walls and are based on summer and winter design conditions. To account for the thermal mass imparted by concrete walls, this software uses hourly weather data for a typical year. The hourly data are commonly used in energy modeling software and are based on typical mean (average) conditions from the past 30 years (TMY2 data). This is more representative of actual conditions in which the HVAC system will be operating. The user can use ACCA Manual S for guidance on selecting equipment after the capacities are determined.
This version of the program incorporates two updates from previous versions related to the heating and cooling system capacities:
1.) The system capacities are based on the heating day and cooling day with the greatest load, repeated for three consecutive days.
2.) The required heating and cooling system capacities have been oversized by 15% for cooling and 25% for heating in accordance with ASHRAE/IESNA Standard 90.1-2007, Appendix G.
Insulated concrete walls are increasingly utilized as an alternative to wood frame walls in residential construction. Insulated concrete walls include insulating concrete form (ICF) walls, cast-in-place insulated concrete walls, insulated precast concrete walls, autoclaved aerated concrete (AAC) walls, and insulated concrete masonry (CMU) walls. Houses constructed with concrete wall systems are both disaster resistant and energy efficient. Energy efficiency is imparted by the inherent thermal mass, high levels of insulation, and low air infiltration of these walls.
Considerable work has been performed by a variety of researchers to compare the energy performance of concrete homes to that of wood framed alternatives. The consensus is that the inherent energy-saving properties of insulated concrete walls can result in HVAC equipment being downsized by as much as 15 to 40% in concrete homes in comparison to identical wood-frame homes.
Unfortunately, widely used HVAC sizing methods such as Manuals J and S and the ASHRAE Handbook of Fundamentals are either cumbersome or do not account for the thermal mass, high levels of insulation, and/or low air infiltration of the insulated concrete walls. Additionally, many builders and HVAC contractors size HVAC equipment based on a 'rule-of-thumb' developed for wood-frame homes that equate equipment size with square footage of living space. The net result is an inefficient HVAC system that is typically oversized. An oversized HVAC system will have a higher initial cost than a correctly sized system, and it will consume more energy than necessary to maintain thermostat set points. Additionally, an oversized system will shorten the 'on' time, which can lead to larger temperature swings and reduced thermal comfort. Air conditioning systems with short 'on' times do not remove enough moisture from the indoor environment, which can promote moisture problems and increase the probability of occupant respiratory problems.
Based on this, the Department of Housing and Urban Development (HUD) sponsored an effort to compile available information regarding energy use in concrete homes, develop additional information as needed, and use this information to develop a methodology to properly size heating, ventilating, and air-conditioning (HVAC) equipment for concrete homes. HUD supports insulated concrete construction because it is energy-efficient and affordable. The result of this effort is an Excel-based program intended for use by residential contractors to estimate the required heating and cooling system capacity for single-family concrete homes. The capacity is based on a user-defined thermostat set point, the house dimensions, construction materials, and location (US and Canada). The software uses the DOE2.1E hourly simulation tool to determine energy loads for equipment sizing.
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