Estudo Geral - Methodology to develop an excel tool aiming at estimating the heating energy demands of the AHUs

Abstract

In many secondary schools in Portugal, indoor air quality is currently assured by mechanical ventilation. In some cases, Air Handling Units (AHUs) are used to supply fresh air at the rooms conditions. Once in the classrooms, thermal loads are suppressed by terminal units, e.g. hot water radiators (used for heating conditions, at 20 ºC). Some heating capacity is also due to a differential temperature between the outdoor air entering the AHU and the supply air into the room. Based upon these considerations and specifically for air-supplying at room conditions, the authors developed an excel tool, aiming at estimating the heating energy demands of the AHUs serving classrooms during an entire scholar year, i.e. the integration of the computed heating transfer rate over the considered period of time. This working file includes the integration of an ‘Energy Plus’ weather file that may vary according to the building site. Therefore, the energy estimations account on the supplied air temperature differential, between the outside air temperature and the desired temperature of the supplied air during the occupancy period. A detailed description of the methodology developed to build this tool – which is mostly rooted on The 2013 ASHRAE Handbook of Fundamentals (Chapter 1) [1] – is next presented.