The importance of outdoor air In air conditioning systems

Mark Knowles BSc. (Hons), Mechanical Engineer • Email: [email protected]

Air Conditioning has become ubiquitous in modern living both in residential and commercial settings. The benefits of Air Conditioning are also well understood, both in terms of comfort and health benefits, as well as on productivity in the workplace. However, in consideration of Air Conditioning for any particular application, there is usually a significant distinction between a residential application and a commercial application. In fact most building codes are very specific to distinguish between residential and commercial guidelines.

One of the major differences between the design guidelines for Air Conditioning is with regards to Ventilation or more specifically “Outdoor Air Requirements for Ventilation”. To grasp the importance of this it is useful to understand one basic principle behind Air Conditioning (AC), and this is that most AC systems are re-circulating systems. This means that the air in a space is circulated by a fan in the space and passed over a cold surface which cools it and sends the cooled air back to the space. This means that the air is circulated over and over in the space keeping it cool. However, during the circulation process other substances accumulate in the air,
these include carbon dioxide and Volatile Organic Compounds (VOC’s). Volatile Organic Compound is a general term that describes any organic substance that can exist in gaseous form mixed with air. VOC’s can come from adhesives, fabrics and other items in an occupied space, which emit small quantities of substances such as Acetone, Ethanol, Ammonia and Formaldehyde. The concentration of these substances as well as Carbon Dioxide can increase over time because of the recirculation of the air by the AC system.

In a residential environment, it is normally assumed that small openings in windows and construction joints, etc. will allow air to infiltrate into the occupied space and this outside air will dilute the contaminants in the air and maintain an acceptable air quality. For this reason and also because of the relatively small size of most residences, most building codes do not mandate ventilation rates and mechanical ventilation for single family residences.

For commercial buildings, however, codes normally mandate a ventilation rate. This ventilation takes the form of outdoor air which is drawn in or forced into a building and mixed with the re-circulating indoor air. Mechanical exhaust is also normally used to remove part of the re-circulating air and balance the system. Contaminants will build up more quickly in a commercial building because of several factors, including more occupants per floor area, larger floor areas and tighter construction.

Increased concentrations of Carbon Dioxide can cause headaches, fatigue, changes in pulse rate and general feelings of ‘stuffiness’ to occupants. This is in addition to several other possible negative health effects associated with VOC’s. We can thus appreciate that outdoor air ventilation is essential to an efficient building and to the health and safety of the occupants. Any gains in occupant efficiency attributable to the AC systems cooling and de-humidifying effects can quickly be eroded if the ventilation is inadequate. Occupant discomfort and health effects will lead to losses in commercial activities.

Some building operators disconnect, disable or block off the fresh air intake into a building, effectively reducing the ventilation to a minimal amount. This is sometimes done with the misguided aim of trying to increase the cooling effect of the AC unit, with the assumption that if the unit makes the space cooler, the occupants will be more comfortable and productive, or to reduce the energy consumption of the system. This often has an unseen negative effect as
noted above. Negative human occupant effects will far outweigh any energy cost reduction if this strategy is employed. It is often better to allow a slightly higher indoor temperature than to compromise the ventilation in a building.

Arguably, the best approach to reaping the best benefits of your AC system is to have the
AC system properly engineered, with calculations done in advance to define the system to be
installed. This will allow proper ventilation rates and ensure a building that operates with the
highest level of efficiency.

The role of the professional in the building industry in a developing or underdeveloped nation

Canute Edd Spencer, FRICS, FCI Arb, MRSH
Email: [email protected]

In attempting to write an article on this subject, one must first define the term “professional in the building industry”, “developing and underdeveloped nation” and perhaps one must also explain why “in the building industry”, are they the only professionals with a contribution
to make?

Last things first, given that I am practicing in the building industry as a Chartered Quantity Surveyor (otherwise known as a Construction Cost Consultant I have been exposed and involved to this industry for many years. Because of my “tenure”, experiences and encounters throughout the years, I believe that I have developed a keen understanding of the subject matter. Equally important is my belief that I cannot or should not attempt to comment on other professionals (e.g. doctors and lawyers) since I believe that there are enough of them to speak for themselves. Additionally, it is worth mentioning that the building industry is the latest recognizable innovation for developing an underdeveloped country.

In my youth, the favored professions were medicine, law and religion. Engineering ran low on the required professional charts as too Architects, we still prefer to use Draftsmen not recognizing the difference, even at the so called sophisticated society social level. Interestingly, the only surveyor known in Trinidad at the time was the Land Surveyor (or “Severere” as locally pronounced).

When I arrived in England in 1959 to pursue Quantity Surveying, it was only then that I realized that there were Land Surveyors, Building Surveyors, Valuation Surveyors, Housing Surveyors, Planning Surveyors and Quantity Surveyors, all of equal importance to and in the building industry.

After completing my studies, I believed (as I do today) that our first responsibility as returning professionals is to educate our society as to our function(s) as well as the limitations imposed upon our efficiency by the sheer circumstances of practicing in an underdeveloped country. For
example, pricing a construction project depends upon an efficient system of collecting data, once the system relied upon is flawed; no amount of qualification on your part can produce correct results.

To be successful, the professional in the building industry (Architect, Engineer or whatever type of construction professional) must consider education as his priority; education of the general public, the various stakeholders within the building industry and the business and financial sectors of our society who should most benefit from our contribution, i.e. mortgagers and financiers. Our role as an educator goes beyond educating the public generally, we are also responsible for the understanding of our fellow professionals with whom we are called upon to work and produce effectively. Specialists are trained to practice within the normal daily purview of their training. In an effort to reduce or even eliminate conflict with their lesser qualified or educated colleagues they must therefore educate themselves and their colleagues on standard practices and new developments as much as possible. With this degree of sharing, the various professionals and even their professions develop daily.

Another important aspect of our education is that of research in local techniques especially since in construction one must apply and understand the theory for its application. For instance in my Construction II class, we were required to provide the solution to a certain construction problem. Out of a class of thirty odd students, only one person produced the right answer, a Trinidadian student who had some experience in the construction industry at home. When asked how he was able to solve the problem, his only answer was “Trinidad construction boy!” However, I always recall that whatever he learnt was correctly learnt and successfully applied away from the English construction climate. In our role as educators, we must also be mentors to our young graduates and craftsmen. This task is easier said than done since many of our consultants are so bent on earning a living that they are not willing to make the necessary sacrifices towards training their locals. Consequently, at the local level we have a list of skilled artisans whose skills are acquired by on the job “pick up” training, which is adequate for some jobs locally but only thus far.

Apart from education, research into our entire building industry, within the Caribbean is also vital to our success. Many years ago, some of us started compiling statistics (on labourers, concrete works, formwork etc.) to apply to the pricing items in the construction industry. However we were advised that this exercise was a waste of time or an exercise in futility since no one would either read or apply it. Sadly, we heeded the negative advice and today we have no statistics on what to base realistic pricing in the industry. In order to emphasize my point that research in local phenomenon, theorized and put in academic form can be the basis of theorizing our local industry for the application of local solution(s) to local problems, consider another example; the ITCA did a complete research study on every type of wood in Trinidad eg. cheynette, mango, cedar etc. identifying all physical characteristics and evaluating its uses, however although this research lies somewhere in our archives, few people know of its existence. Maybe, as professionals we also need to develop some system to prevent knowledge from being lost from lack of use (which could result in the said research being redone) and maintained in some permanent manner.

My era of returnees bombarded every financial institute eg. lending agencies and the general public with quantity surveying  formation. Our approach included our fellow professionals i.e. Architects, Engineers and any other group involved in planning and organizing any aspect of the industry. As a result, today we have a much more knowledgeable cadre of building professionals who should now be more efficient in servicing the general public and financial sector. However our responsibility as professionals does not end here.

Our next challenge is to replace external examinations such as City and Guilds, Clerk of Works examinations, Institute of Builders etc. with similar local programmes which are overseen by local examining board consisting of our professionals who would have designed and compiled the syllabus.

Finally, professionals must reflect a high level of integrity in not only their everyday conduct but in their professional demeanor and practice. We must earn the respect of our community both professionally and generally. Dignity is not handed to you because you are a professional. You must earn it by your general conduct and all its members must be a party and comply with the necessary requirement. Having been a member of the building industry for nearly 50 years, I strongly believe that professionals in developing countries must:

a. Educate the public and their fellow professionals as to their function.
b. Train not only your fellow professionals but all the subsidiaries in your field. It is an investment well made.
c. Conduct research in all aspects of your profession so that one’s performance and its basis must be recorded to be in a form to be passed on and
d. Finally, strive to achieve integrity in both general and professional behaviour.

When we have developed a culture of knowledge sharing and mentoring, issues like research and development as well as professional development progress naturally finally resulting in the growth and development of the building industry.