User:MiaoLiBerkeley/sandbox

A Personal Comfort System (PCS) is an arrangement of devices which, without supplying outside air, heats or cools a building occupant to produce thermal comfort at ambient temperatures below or above neutrality for the person. The term concerns only the thermal aspect of personal environmental control (PEC) - a broader concept also covering personal ventilation (PV) which involves air exchange with the outside. It should be noted that systems which manipulate air circulation indoors for personalized thermal control without significantly introducing outside air (e.g. electrical fans) are included in the definition of PCS. Uses of the term personal comfort system (or conditioner, device etc.) in a loose sense date back to patents issued in the 1990s. Currently most academic research papers touching PCS discuss in effect its supercategory- PEC.

Historical Background
Most traditional methods of indoor environmental control before the modern HVAC involve PCS. For example, an open fire is a source of radiant heat whose experienced intensity can be controlled by moving toward or away from it. The fire does not heat up every space of the room or the building equally. The concept of PCS is best appreciated in the context of today's central HVAC systems and of the resulting assumption that all spaces should have a more or less uniform temperature. The idea of local, personalized environmental control was first captured in the term "task-ambient conditioning" (TAC), which draws on an analogy with task-ambient lighting. A working committee of researchers and manufacturers in the indoor environment field decided in 2008 to favor the term ‘PEC’ over ‘TAC’. The term Personal Comfort System was formally defined first by University of California, Berkeley researchers Hui Zhang, Edward Arens and Yongchao Zhai in a seminal paper written in 2015.

Grounds for effectiveness
Currently most researchers agree that PCSs are beneficial for comfort and energy reasons. However, there is variance of views over the relative prevalence of physical contribution and psychological effects of personalized systems in producing thermal comfort. A greater understanding of the influence of personal control has implications for building design, occupant comfort, and energy use.

Thermal comfort
PCS has the potential to satisfy individual comfort requirements, as interpersonal differences in thermal sensation due to age, sex, body mass, metabolic rate, clothing and thermal adaptation can amount to an equivalent temperature variation of 2-5 K, which is impossible for a central, uniform HVAC system to cater to. Nevertheless, there is strong empirical evidence that people's perceived ability to control their thermal environment improves their thermal comfort. Such a finding corroborates the adaptive thermal comfort hypothesis proposed by Brager and de Dear (1998).

Energy conservation
PCS can lower the energy consumption of HVAC systems, as it takes much less energy to heat or cool individual building occupants than the entire air mass inside the building uniformly.

Types of modern PCS
Zhang, Arens and Zhai (2015) provided a list of generalized types of PCS. These types are as follows :

Head/ face/ upper body local air jets
This category includes desk fans, small USB fans, nozzles and slot diffusers in desks and and workstation partitions. Air flows are usually frontal or from the side. Specific PCS products incorporating these features include the ‘Personal Environmental Module (PEM)’, ‘ClimaDesk’, and the Exhausto personal ventilation system (this is strictly speaking not a PCS due to the introduction of outside air).

Overhead (ceiling) fans
These provide a vertical air-stream under the fan which grades to a lateral stream outside the air jet. A wide variety of fans are commercially available. Their power efficiency and acoustical quality has been greatly improved in recent years due to improvements to their motors (now often brushless and direct-current) and fan blade designs.

Large-area lateral air flows
Large box fans produce such bulk airflow, typically seen in industrial, gymnasium, or lobby settings. Natural airflow through windows or open designs may resemble such flows.

Heated or cooled seats
Chairs have been heated using electric resistance heating elements in the seat surface, the warm side of thermoelectric devices, or with warm water tubes. Chairs have been cooled using isothermal air convection through or behind the heat surface, contact surfaces connected directly to the cool side of thermoelectric devices, and through cooled water tubes. Most commercial examples to date have been in the automotive industry, where cooling is convective using cooled air from thermoelectric devices or the automobile's central HVAC.

Footwarmers, legwarmers, kneehole radiant panels
The lower extremities (feet and legs) can be heated by radiant sources (panels or focused sources such as reflector bulbs), or less efficiently by conductive pads under the feet.