PEAK Institute

UV light is high energy enough to disrupt the cellular bodies of microbes. The particular wavelength used in these lamps is not the “sunburn/skin cancer” spectrum, but has been shown to cause acute damage to the eye, so care should be taken to prevent building occupants and operators from looking directly into these lamps when operating. This wavelength can also be tough on colored finishes and plastic, so care should be taken to keep these lamps from shining directly on these materials and finishes.

UVGI inside an air handler, shining UV light on the cooling coil is an application to reduce biological fouling of cooling coils. Reducing the amount of accumulated material on these coils both improves the heat transfer of the coils and reduces the pressure loss of air flowing through them. Because the UV dosage time is very short for any airborne microbes that aren’t actually stuck to the coils, air handler UVGI isn’t of much good for “killing” airborne infection.

Upper room UVGI application depends on the geometry of the room. The ceiling height in rooms must be great enough so that there is volume for the room air to circulate up into the “kill zone”, and for the light fixtures to be mounted high enough to keep line of sight from occupants below, so, generally speaking the fixtures should be mounted at least 8 ft above the floor and the ceiling should be at least 2 ft above the fixture in order to create space for air to circulate in the volume above the fixtures. Upper room UVGI is best applied in large rooms where the air circulation patterns allow for mixing. We have applied upper room UVGI in emergency department waiting rooms, for instance. This technology has not been shown to be particularly effective against the SARS-CoV-2 virus, however. The half-life of these airborne aerosolized viral particles is so short (a few hours at most) that they will probably naturally degrade before they can circulate up into and spend enough time in the UV “kill zone” to actually be inactivated by the upper room UV.

In the AEC industry we often focus on the indoor thermal comfort of occupants. Many designers use exterior spaces for transition between buildings on campuses or retail establishments. Foot traffic drives retail, and retail drives the success of many project types. Making customers traversing the outdoor part of a development comfortable is just a matter of taking the skills used to create comfort indoors and applying these principles to the outdoor space. The creative use of shading, air movement, daylighting, heat reclamation, and humidity management can make these outdoor spaces slightly more comfortable. Utilizing exterior spaces for some of this program also reduces the energy impact of the buildings because that area no longer has to be heated, cooled, or ventilated.

TLC uses computational fluid dynamics simulations in conjunction with large scale solar shading analysis to inform strategies for creating comfortable outdoor spaces. Rather than using ASHRAE 55, which is used for indoor thermal comfort analysis, the Universal Thermal Climate Index (UTCI) is used to quantify the effective outdoor comfort criteria. Most people are familiar with its use in weather forecasts to indicate what temperature the weather feels like from the effects of wind speed, temperature, and humidity.

Not only does it take energy to create the light, the inefficiency of the bulb turns the unused electricity into heat, which is removed by the HVAC system. Adding those two power usages together highlights the significance of energy used by lighting systems.

In addition, lighting is a primary driver of health. Recently discovered health findings show that not all light stimulus on the body creates visible signals in the brain. The intrinsically photosensitive retinal ganglion cells (ipRGCs) in the eyes, discovered in 1923, have only recently begun to be understood fully, including how they play a role in synchronizing the circadian rhythms of the body.

The body responds to color and intensity of light. In some cases the lack of adequate lighting can contribute to Seasonal Affective Disorder (SAD) and other disorders. Circadian lighting is an effective tool in places with limited access to outdoor views, such as Newborn Intensive Care Units (NICU), office areas, back-of-house workspaces in hotels, and other spaces. Design now takes accessibility of full spectrum daylight into account when designing lighting spaces, setting targets not just for lighting power density, but also color and intensity.