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Fan coil units (FCUs) are decentralized air-conditioning devices to locally condition zone air. In the U.S. and Europe, FCUs are widely deployed in diverse types of buildings such as offices, hotels, schools, and residential apartments because of their low cost and easy installation. The abnormal operation of FCUs due to faults or malfunctioning components may cause significant energy waste and degrading thermal comforts. However, faults occurring in FCUs have been seldom investigated. A systematic analysis of fault impacts of FCUs would enable a better understanding of fault impacts, an efficient development of fault diagnostics approaches, and an improvement of FCUs monitoring system design. In this paper, we used a FCU simulation model, which was developed in the HVACSIM+ environment from a previous study to evaluate FCU fault impacts. Five common faults with different intensities were simulated within a one-year time window to generate fault inclusive operation data. We employed a bottom-up fault impact analysis framework. Fault effects on multiple measurements were firstly evaluated to obtain fault symptom occurrence probability distributions which quantify measurements' sensitivities. Secondly, fault thermal comfort impact and fan power energy consumption impact were assessed. Lastly, the result from fault thermal comfort impacts and energy penalties was used to rank FCU faults. [ABSTRACT FROM AUTHOR]

Task-ambient conditioning (TAC) systems have proven success in reducing power consumption, improving thermal comfort and enhancing air quality. However, the adoption of TAC has, however, been generally slow. We propose an improvement to TAC systems by disconnecting them from the central air-handler, effectively making them ductless. The Ductless Task Air- Conditioner (DTAC) utilises thermoelectric modules and phase change materials for heat exchange and heat sink respectively. Prototypes of DTAC have been developed concurrently with test regimes for the proof of concept. The paper also presents the technical studies performed on the prototypes to show its capability and limitations. Whilst still in its early stages, DTAC shows promise for delivering supplementary air-conditioning to office occupants, conserving overall air-conditioning by allowing the central air-conditioner to have a higher temperature set-point and increasing occupant thermal comfort by allowing them to have direct control over their immediate thermal environment. [ABSTRACT FROM AUTHOR]

The objective of this field investigation was to compare the impacts on thermal comfort due to vertical location of return air inlets in a residential forced-air system operating in the cooling mode. Design guidelines for forced-air cooling systems recommend placing return air inlet locations above the occupied zone in order to improve circulation of stagnant air and reduce thermal stratification. A companion study of the heating mode is under way. Results from the research will be used to recommend optimal return air inlet locations for year-round performance. An energy-efficient three-story house in Pittsburgh, Pennsylvania, was used as the test site. A single HVAC system, zoned by floor, was operated at a constant setpoint temperature of 72°F (22.2°C) throughout the investigation. The vertical locations of return air inlets were modified using temporary cardboard ductwork to create two distinct cases for the investigation—one with high returns and one with low returns. Two central data acquisition systems were used to measure system parameters and multiple space temperatures throughout the house on a minute-by-minute basis. The room air temperatures were compared to the requirements of ASHRAE Standard 55 (ASHRAE 2004b) for thermal comfort and recommendations of ACCA Manual D (1995) for uniform temperatures between rooms. Room air temperature stratification for all rooms and all hours was found to be well within ASHRAE guidelines. Although pressure imbalances between spaces were not the focus of the investigation, they appear to have been the driving force of air leakage at zone temperature sensor locations, contributing to room-to-room temperature differences that exceeded ACCA guidelines. Evaluation of the data leads to the conclusion that high return air inlets help reduce stratification in spaces with floor diffusers. However, vertical location of return air inlets appeared to have no impact on cooling performance in spaces with ceiling supply air outlets. [ABSTRACT FROM AUTHOR]