100% Outside Air Systems – Passive Radiant Cooling & Heating Systems
Passive radiant heating and cooling system designs exploit the properties of all heat transfer modalities for enhanced system efficiency and healthier built environments.
In the concluding paragraph of the Oct. 7, 2021, Engineered Systems’ article titled, “Health Care Design: Beyond Code Minimum – Creating Healthier, More Efficient Environments,” it was proposed: “Physical laws can also be exploited to contribute to workload reduction to meet health care HVAC needs…” Understanding the physical laws of heat transfer — i.e., evaporation (vapor compression cycle or evaporative cooling) and conduction (coil heat transfer) — to effectively transfer discrete amounts of energy to or from a building is a given. HVAC designs apply the laws of physics to calculate building cooling and heating loads and, there upon, the amount of energy required to execute the work to be done to maintain stable, comfortable, and healthy building environments. It is not uncommon for engineers to then add a 15%-20% contingency to ensure system layouts have enough energy available to overcome loads that were not anticipated and/or other operational variances. The statement’s intent was to convey the idea that a mechanical brute-force approach to heat transfer is not the only available methodology. A design team can adopt another mindset that passively applies, at least partially, to all methods of heat transfer in a manner that will reduce the amount of system work to be done.
Dedicated outside air systems (DOAS) offer design teams such an approach when applied to passive hydronic HVAC systems. Unlike conventional designs that apply only two heat transfer modes, evaporation, and conduction, engineering teams can propose more efficient systems by exploiting all four natural heat transfer methods: conduction, convection, radiation, and evaporation. This article will review and evaluate passive radiant heating and cooling systems as an effective design approach that exploits the properties of all heat transfer modalities for enhanced system efficiency with the added benefit, when properly designed, of creating healthier built environments.