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HVAC Thermal Comfort PowerPoint PPT Presentation


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What's the number one customer complaint about their facility? "The office is too cold." What's a close number 2? "The office is too hot." If you outsource your system and H/C (hot-cold) calls, or are the service provider for them, it is important to understand the issues behind these complaints. FMs and suppliers know that H/C calls cannot be handled quickly and uniformly with one technical solution. Solving H/C calls requires an in-depth understanding of technical HVAC systems, of the factors contributing to human thermal comfort, and of the unique physiological needs of building occupants.Indoor thermal comfort is dictated by the building and its occupants. The building has specific design criteria and limitations based on outdoor conditions, space usage and system capabilities. Occupant comfort is influenced by the tasks performed, metabolism, age and other personal and physiological factors. Occupants expect the building's HVAC system to provide continuous thermal comfort, allowing them to do their jobs. Between the building and the occupants, a facility manager must continually strive to provide thermal comfort in a seamless, invisible manner to let workers be productive and uninterrupted by thermal discomfort. THE TECHNICAL SIDEThe technical standard for thermal comfort comes from ASHRAE (American Society of Heating, Refrigeration and Air-conditioning Engineers). According to ASHRAE the acceptable operative temperature range from 68 to 74 degrees in the winter and 73 to 79 degrees in the summer. Other considerations are how metabolic rates and clothing impact thermal comfort. ASHRAE considers a number of mechanical equipment operating conditions to impact a thermal environment. THE PRACTICAL SIDEWhile the technical side provides an insight into the system requirements and human needs for thermal comfort, in the practical daily operation of a facility, it rarely resolves an occupant complaint.

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HVAC Thermal Comfort

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Hvac thermal comfort

What's the number one customer complaint about their facility? "The office is too cold." What's a close number 2?

"The office is too hot." If you outsource your system and H/C (hot-cold) calls, or are the service provider for them, it

is important to understand the issues behind these complaints. FMs and suppliers know that H/C calls cannot be

handled quickly and uniformly with one technical solution. Solving H/C calls requires an in-depth understanding of

technical HVAC systems, of the factors contributing to human thermal comfort, and of the unique physiological

needs of building occupants.

Indoor thermal comfort is dictated by the building and its occupants. The building has specific design criteria and

limitations based on outdoor conditions, space usage and system capabilities. Occupant comfort is influenced by the

tasks performed, metabolism, age and other personal and physiological factors. Occupants expect the building's

HVAC system to provide continuous thermal comfort, allowing them to do their jobs. Between the building and

the occupants, a facility manager must continually strive to provide thermal comfort in a seamless, invisible manner

to let workers be productive and uninterrupted by thermal discomfort. There are two main sides to thermal comfort -

the technical (1) and the practical (2) side.

THE TECHNICAL SIDE

The technical standard for thermal comfort comes from ASHRAE (American Society of Heating, Refrigeration and

Air-conditioning Engineers). According to ASHRAE the acceptable operative temperature range from 68 to 74

degrees in the winter and 73 to 79 degrees in the summer. Other considerations are how metabolic rates and clothing

impact thermal comfort. ASHRAE considers a number of mechanical equipment operating conditions to impact a

thermal environment.


Hvac thermal comfort

THE PRACTICAL SIDE

While the technical side provides an insight into the system requirements and human needs for thermal comfort, in

the practical daily operation of a facility, it rarely resolves an occupant complaint. It is how a hot-cold (H/C) call is

handled that is important, rather than what is done. The practical daily applications of technical principles along with

the client service aspects for H/C calls involve more than just engineering savvy.

The practical handling of client thermal discomfort involves PR (public relations) work, education, patience and

hand-holding. It is not always the technical fix, but the client's perception and need for an immediate solution that is

paramount. With productivity issues becoming more important, environmental discomfort is seen as an unnecessary

nuisance and a disruption to business operations.

Many FM operations and maintenance workers consider H/C calls to be the nemesis of their daily operations. They

all know the constant whiners that always complain about being too hot or too cold. FMs even wrongly believe that

women complain more about thermal comfort than men, even as studies show this is not true. Maintenance workers

will sometimes delay their response to H/C calls for certain problem areas. Such delays usually make things worse,

and are a bigger part of the H/C call issue than the initial problem. Customers are usually more perceptive than

HVAC workers realize. FMs and suppliers need to tactfully educate customers rather than sidestep the issue.

There are various reasons behind H/C calls: Work task, activity level, clothing, temperature, humidity, air flow,

worker and equipment age, T-stat location, solar gains, system design parameters, end-of-duct run, etc.

The ideal response to a H/C call is to react as quickly as possible and to educate the customer on the boundaries

within which the FM department is operating. They need to explain what the occupants can do themselves to

alleviate some of their discomfort, whether it's changing workstation or work place location and wearing different

clothing, to providing capital funds for a retrofit. Some of these solutions are temporary at best, and need to be

identified as such.

In analyzing a H/C call, many FMs point the finger at the initial mechanical engineering design and the

commissioning (or lack of commissioning) of the HVAC system. In the initial HVAC system design, there are

numerous system variations from which the engineer can choose. The selection of the HVAC system is usually

based on climate, structure type, energy costs, initial and annual costs, availability and owner preference. In retail

environments, HVAC systems are essential to attract customers and keep them comfortable. In large office

buildings, perimeter and core issues drive the design. Other considerations such as automatic controls, zoned air

distribution, outdoor air and humidity levels are also optimized in the design selections. In general, the simpler and

more optimally sized, the less maintenance and operating cost for a given HVAC system. In office buildings, since

everything is duplicated many, many times, minor design variations can substantially affect construction and

operating costs. Changes in occupant usage, occupant installed space heaters, taping of diffusers, and changes in

local construction after the HVAC system is installed and operating are major issues and contribute to many of the

problems associated with H/C calls.

SOLUTIONS

To solve H/C calls and thermal comfort issues, a performance-based expectation of building occupants may be the

best approach: keep occupants comfortable at all times. The reality of handling H/C calls is more complex. By

understanding what human thermal comfort is and what a building's technical systems' capabilities and limitations

are and by focusing on educating customers, FMs and suppliers will have a higher likelihood of success in solving

H/C calls. The HVAC suppliers need to get involved in addressing the physiological needs of the building

occupants, as much as providing the proper technical solutions.


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