Much like office practices and workflows, modern offices are changing. They are designed to be more open than in the past, which consisted of a ring of private cabins or offices surrounding clusters of cubicles in the centre of the office floor. The open plan design calls for alternative considerations for heating, ventilation and air conditioning, or HVAC duct design.
Cubicles are increasingly replaced with workspaces created for specific activities, such as team lounges, fitness centres and large work tables for discussions and collaboration on team projects. The HVAC system consumes a significant portion of all energy needs in a building, and changes in the office layout will impact the HVAC design. Thinking and planning for HVAC design in an office space needs to begin as early as possible when considering renovation or a new project to save energy costs.
Design goals for office buildings are based on the fundamental principle of ensuring health and safety to those occupying those buildings. Ventilation, therefore, is required at all times and must eliminate or minimise pollutants. The measure of air flowing in or out of a space is cubic feet per minute or cfm. Generally, a person needs up to 30 cfm of outdoor air, and an ideal comfortable temperature is between 20 and 24ºC with 20-60% relative humidity. The efficiency of HVAC systems design makes these conditions possible.
Some of the key strategies for efficient HVAC systems design in modern offices include:
Reduction of Cooling Loads
Well insulated walls, floors and windows are a must. The use of natural light for a healthier workplace is becoming increasingly accepted as the norm and for the reduction of heating loads during the winter season. For warmer climates, tinted low-e glass can help avoid solar gain (solar heat gain or passive solar gain), which is the increase in thermal energy resulting from the absorption of solar radiation, and reduce cooling loads. Low emissivity glass, or low-e glass has a super-thin transparent coating that reflects infrared energy or heat. This glass minimises both ultraviolet and infrared light passing through it without affecting the visible light that is transmitted.
Lights that automatically switch off during sufficient daylight conditions are a useful energy-saving idea, which can work as a complement to cooler lighting options and will generate less heat, thus reducing cooling loads on the HVAC system.
HVAC System Size
It’s important not to install an HVAC system that is too big for the energy needs of the office concerned. Oversized air conditioning systems typically create discomfort during the day. Such systems generally switch on and off continuously and are not efficient in removing humidity, resulting in an office area that is predominantly humid and dotted with hot and cold spots. More than just square footage needs to be considered in calculating HVAC load requirements. Computer simulation can accurately analyse building materials, daylight, lighting design and space activities affecting HVAC loads.
Multiple zones with independent temperature controls within a large open space translates to greater efficiency and comfort. Different areas in open spaces have different temperature requirements, such as:
- Perimeter areas, which need separate controls, as they are more susceptible to weather
- Computer rooms, which have special temperature needs and controls
- Conference rooms and other areas that host large gatherings of employees, which need more cooling while in use and less when empty
Modern offices with fewer internal walls make these design details tricky.
Smart buildings use sensor technology, mainly with two types of sensors – light sensors and occupancy sensors. These can be incorporated with HVAC design early in the design stages. Light sensors sense the amount of daylight available and adjust lighting accordingly. They can be connected to the HVAC system to maintain heating and cooling. Occupancy sensors track the number of people in a given space at a given time. They communicate with HVAC controls to regulate temperatures. During a large meeting, for example, occupancy sensors help increase cooling for the area concerned.
A ‘Sensible’ Option
Environmental sensors lead to cleaner, healthier air. Sophisticated sensors provide real-time data on air quality, revealing the surprisingly unhealthy current conditions of most offices worldwide and a related reduction in productivity. Studies show that a 670-sq ft office with 15 employees can generate CO2 levels of 1,000 parts per million (ppm) in under 8 hours. This is equivalent to 2.5 times atmospheric carbon dioxide levels and at a level that may cause 15% decrease in cognitive performance in employees. Meeting and conference rooms, naturally, are even worse, with 3,000 ppm, significantly decreasing productivity.
Organic compounds from furniture and carpets combine with these high levels of carbon dioxide to increase fatigue in employees and decrease productivity. In some cities, windows cannot be opened due to the toxicity of the smog outside. Indoor air quality could be improved with HVAC systems that react to carbon dioxide and airborne particles. This could be achieved by pulling in fresh air and filtering out pollutants.
Under-floor Air Distribution
Typically, air conditioning cools a space using overhead air distribution. This method may not be ideal and less energy efficient in open spaces with high ceilings. Use of under-floor air distribution is a popular trend today. Diffusers are installed under a raised floor, transmitting cool, air-conditioned air throughout the space. Stratification moves warm air upwards to the ceiling and cooler air-conditioned air replaces it at ground level. This method has been found effective in providing continuously comfortable conditions and maintaining better air quality.
An effective HVAC design must control humidity, eliminate odours and remove dust, carbon dioxide, bacteria and viruses that may contaminate the space and spread illness. In an open-plan office, this is critically important. The correct indoor air quality must be regulated and maintained for the well-being of employees and their productivity. Sufficient intake and distribution of outside air and the controlled circulation of conditioned air is a mandatory requirement of efficient HVAC design.
Whether renovating or creating from scratch, professionals from the field, such a HVAC mechanical engineering consultants, must be taken on board right from the early stages to avoid costly errors at later stages. Consultants will utilise their professional HVAC design and drafting skills to produce high quality HVAC shop drawings, which can then be coordinated with other trades.
Decades ago, offices had windows that could be opened. Currently, most offices worldwide are air conditioned and air tight. Windows that can be opened help control energy consumption and give people greater control over their work environments. But skyscrapers with offices don’t have windows that open or have access to fresh air during a work day. Why? Well, some of the reasons for permanently closed windows are:
- To prevent cooled, air-conditioned air from escaping and unfiltered air, noise, rain and insects from entering
- That offices are wary that people may fall out or jump out, resulting in the offices and management being held responsible
- That some employees may open windows on a hot day, making the air conditioner work harder
- That in keeping with modern architecture, open windows are unfashionable and they disturb the lines of the building
- That with many employees on any floor, natural ventilation is near impossible
- That energy is saved, increasing productivity
Facts show that these concerns are no longer concerns. A naturally ventilated, intelligently designed office building can halve the energy consumption of constantly air-conditioned buildings. A naturally ventilated building need not support intense and constant HVAC system needs. Ventilation that is natural and access to fresh air contributes to an increase in productivity. A connection to the outdoors, a perception of control and better overall health are beneficial side effects of natural ventilation. The design of HVAC systems in an office facility thus has a direct bearing on the productivity of the office’s inhabitants.
With the help of qualified and experienced HVAC mechanical engineering consultants, a comfortable, safe and secure office building may be constructed with the right HVAC shop drawings. In the global environment of outsourcing MEP (mechanical, electrical, plumbing) design services, the quality, expertise and experience required can be found overseas, resulting in cost-effective, precise HVAC design and drafting.