Forrest Meggers

The feasibility of performing high-temperature radiant cooling in tropical buildings when coupled with a decentralized ventilation system

In Singapores hot and humid environment, air conditioning has moved from being perceived as comfort to now being a necessity. Buildings usually employ large energy-consuming air systems to condition interior spaces. The use of water-based high-temperature cooling concepts is hard to find due to fears of condensation. The objective of this research is to enunciate the decentralized approach adopted in performing space cooling and dehumidification. The experiment aims at understanding the practicability of using radiant panels with high-temperature chilled water for accomplishing sensible cooling coupled with an independent ventilation system for achieving latent dehumidification. The dew point temperature of air surrounding the radiant panels is monitored to check for condensation. The decentralized ventilation system tested was effective in reducing absolute humidity in air from 22.3 g/kg in outside air to 12.8 g/kg at the under-floor air distribution systems diffuser outlet. The associated dew point temperature and dry bulb temperature measured at the diffuser outlet was 13.9°C and 19.9°C (57°F and 67.8°F), respectively. The measured dew point temperature of air surrounding the radiant panels was 18.3°C (64.9°F), which demostrates the viability of operating radiant panels using high-temperature chilled water to achieve sensible cooling. The air exchange effectiveness of the system running at low supply air velocity was determined to be 1.12, which demonstrates a displacement ventilation system. The air change rates measured per hour using tracer gas techniques ranged between 0.9–2.2 when the supply fan speed was varied between 4000–8000 rpm. The amount of outdoor air thus supplied to the designed space ranged between 0.9–2.1 L/s-m2 (assuming the system ventilation efficiency as 1). These values are above 0.7 L/s-m2, which is the minimum requirement for ventilating office spaces according to Singapore standards.

The reference environment: utilising exergy and anergy for buildings

The utilisation of exergy and anergy concepts for low exergy system design extends the potential of performance optimisation of buildings. We propose a new perspective for buildings and their external environment. It recognises exergy as the utilisable potential that maintains comfort inside relative to outside ambient conditions. It considers environmental heat sources as a form of transiting exergy that is utilised internally to increase second law effi ciencies and then returned to the environment. These sources are not chosen to optimise energy inputs, but rather temperature inputs. They are optimised as anergy sources coming from a dispersed state, which are transited through the building system and deposited back in an anergy sink, which defi nes the reference environment. A major obstacle in the application of exergy analysis to buildings is the lack of an accepted defi nition of the reference environment. The absence of this factor leads to ambiguity in analysis and hinders comparisons between studies. Choosing the reference environment infl uences the amount of exergy contained in buildings and with the low quality levels often dealt with in buildings, the infl uence can be signifi cant. The perspective we present clarifi es the use of the ambient environmental conditions as the reference environment for exergy analysis of whole buildings. It also validates the unencumbered use of free ambient anergy sources from the ground, water, air and the sun to increase exergetic performance.

Sensing of Indoor Air Quality—Characterization of Spatial and Temporal Pollutant Evolution Through Distributed Sensing

Discouraged by the high-cost and lack of connectivity of indoor air quality (iAQ) measurement equipment, we built a platform that would allow us to investigate what kinds of iAQ evolution information could be collected by a low-cost, distributed sensor network. Our platform measures a variety of iAQ metrics (CO¬2, HCHO, VOC, NO2, O3, Temp., RH), can be flexibly powered by batteries or standard 5W power supplies, and is connected to an infrastructure that supports an arbitrary number of nodes that push data to the cloud and record it in real-time. Some of the sensors used in our nodes generate data in standard units (like ppm or °c), and others provide an analog signal that cannot be directly converted into standard units. To increase the relative precision of measurements taken by different nodes, we placed all 6 pairs of the nodes used in our deployments in the same environment, recorded how they reacted to changing iAQ, and developed calibration functions to synchronize their signals. We deployed the comparatively cross-calibrated nodes to two different buildings on Princeton University’s Campus; a fabrication shop and an office building. In both buildings, we placed nodes at key positions in the ventilation supply chain, providing us with the ability to monitor where indoor air pollutants were being introduced, and when they tended to be introduced – enabling us to monitor the evolution of pollutants temporally and spatially. We find that the occupied space of the fabrication shop of the first building and the open plan office of the second building have higher levels of volatile organic compounds (VOCs) than outside air, indicating that both buildings ventilation system is unable to supply enough fresh air to that space to dilute VOCs generated inside. In the second building, we also find indications that other parameters are being driven by set-backs and occupancy. These first deployments demonstrate the ability of low-cost distributed iAQ sensor networks to help researchers identify where and when indoor air pollutants are introduced in buildings.

Hidden Surface Effects: Radiant Temperature as an Urban and Architectural Comfort Culprit

The movement of heat throughout our built environment by transmission of radiation between surfaces is often overlooked in the operation, performance, and comfort of buildings. The temperature of a surface determines the amount of blackbody radiation it will emit, and thus controls the radiant exchange of heat in the environment. The heat exchange by radiation is important for systems and can dramatically influence the energy efficiency and the perceived comfort of a building. We discuss the physical mechanisms for measuring and understanding the heat transfer by radiation in buildings as well as the important connections to system performance and operation. The historical perspective on comfort, operation, and radiation is discussed. Finally, some novel concepts that take advantage of an understanding of radiant heat transfer potential are explored.