Welcome to the solutions page

By Grant Laidlaw

Many people ask for assistance in understanding theoretical and practical aspects of the industry. I will endeavour to enlighten. We are going back to basics as I have questions coming in that indicate that the basic understanding necessary to work in industry is not in place.

Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy (ACRA) in Edenvale. He holds a Bachelor of Business Administration and an associate degree in educational administration. He has a National TechnicalDiploma and completed an apprenticeship with Transnet. He has dual-trades status: refrigeration and electrical. He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018. Currently he is the SAIRAC national treasurer.

Hi Deon. While it is true that the air conditioning system does clean and cool the air, the issue is more complex than this. In addition to cleaning and cooling one has to maintain the quality of the air. We are primarily referring to oxygen levels, humidity, odour and contaminant levels. In your example the people in the room use the oxygen when breathing and release carbon dioxide. As your unit is only recirculating the same air, over time the oxygen levels decrease, and carbon dioxide levels increase. Odour levels may increase. The air becomes stale. This is an unhealthy situation with people becoming drowsy, getting headaches and experiencing general fatigue. What is needed to rectify this situation is fresh air ventilation from outdoors.

Fresh ventilation air replaces oxygen, removes the carbon dioxide, contaminants and odours. In fact, most correctly designed buildings will have a minimum fresh air intake of 10%. ASHRAE has published recommended tables for fresh air rates expressed in air changes per hour. An office for example should have around six air changes per hour. In other words, the ventilation system should supply fresh air six times the volume of the room every hour.

This is a common situation with unitary air conditioning systems installed without regard to fresh air intake. Installers simply rely on natural ventilation through open doors and windows. In certain circumstances this becomes more critical. In a boardroom, for instance, there may be several people present who close doors and windows for a meeting that spans several hours. The air will rapidly become ‘stale’ in this situation.

Hideaway units, as well as cassette units, often have the facility to install fresh air intake and this should be used. In this way you will be able to condition the air as well as maintain air quality. Remember as you are now adding extra air into the room there will be slightly positive pressure. This is advantageous as the fresh air is filtered and dust will not enter the room. Due to the higher pressure in the room, air tends to leak out, preventing dusty air from entering. At the same time remember that you must ensure that the air has some path to exit the room. Small door grills or even undercut doors should suffice.

DEEP DIVE INTO VENTILATION

Let us have a deeper look at ventilation.

As you noted, the terms ‘ventilation’ and ‘air conditioning’ are sometimes confused. All air conditioning systems should incorporate a ventilation system of some form. The essential requirement of a ventilation system is to replace the contaminated air in a particular area with fresh outdoor air.

The purpose of ventilation is to freshen up the air inside buildings in order to achieve and maintain good air quality and thermal comfort. Ventilation also has important psychological aspects, which can be illustrated by the feeling of being in control, having odour management and creating a link to nature.

The quality of indoor air influences humans in several ways:

• Comfort: the pleasantness of the air is immediately felt when a person enters a building
• Health: breathing poor indoor air with lowered oxygen and increased carbon dioxide levels can have negative health effects
• Performance: high-quality indoor air can improve mental performance and general well-being
• Nature: fresh air creates a link to the outdoor environment, and fresh air through windows is a valued aspect of ventilation

Indoor air contains many different compounds, some of which have a negative impact on health or comfort:

• Gases: for instance, formaldehyde, organic chemicals and inorganic chemicals
• Particles: for example, dust and combustion products
• Radioactive gas: such as radon
• Biological: for example, mould, fungi, pollen and dust mites
• Water vapour: or humidity

Most of the pollutants come from sources indoors, from:

• Human beings and their activities: particles from cooking, products for cleaning and personal care, consumer electronics and electrical office equipment
• Building materials: thermal insulation, plywood, paint, furniture and floor/wall coverings

From outdoor sources, there is pollen, traffic and industry. Radon exists naturally in the ground and enters the building through the floor construction. It is important to use the principle of source control to minimise the concentration of pollutants in the indoor air. To better understand the impact of indoor air on our health, we need to consider the amount of air we breathe per day. An average person consumes 2kg of food and water a day, but breathes in 15kg of air a day (12 000 litres). The health impact is clearly important.

On average 90% of our time is spent indoors, so most of the air we breathe comes from indoor environments. The individual or combined effects of the many compounds in indoor air on human health are not fully understood, but major research studies have shown that indoor air quality has an  important impact on the health of humans in buildings.

Sick building syndrome

The term Sick Building Syndrome (SBS) is used to describe situations in which building occupants experience acute health and comfort effects that appear to be linked to time spent in a building, but for which no specific illness or cause can be identified. The complaints may be localised to a particular room or zone or be widespread throughout the building. As can be seen from the chart below, ventilation has the highest impact.

The symptoms of these problems include headaches, eye, nose or throat irritation, dry cough, itchy skin, fatigue and concentration difficulties. These symptoms are defined as SBS symptoms, and the World Health Organisation (WHO) concludes they are found in 15-50% of all buildings. A review showed that air-conditioned office buildings have a 30-200% higher prevalence of SBS than naturally ventilated buildings. The symptoms are believed to be caused by poor indoor environments and can be helped by improving the air quality.

Living or working in damp buildings are among the indoor air quality factors that are most likely to cause illnesses.

Investigations into thousands of buildings have shown that damp buildings can cause illnesses such as coughs, wheezing, allergies and asthma. A damp building is a building with an increased humidity level (the exact risk level of humidity is not known).

Investigations on the mental performance of occupants in office buildings and schools have shown that poor air quality reduces mental performance, while good air quality improves performance.

Deon, there are several ways to bring fresh air into our homes. Ventilation systems can be natural, mechanical or hybrid (a combination of the two). There are two ways to ventilate or cool buildings, namely; actively or passively.

• Active ventilation or cooling – this refers to systems where mechanical components or other energy-consuming components such as air-conditioning systems or fans are used.
• Passive ventilation or cooling – this is a technology or design feature used to ventilate and or cool buildings with no energy consumption such as natural ventilation by open windows. Passive cooling is a measure that consumes no energy to cool buildings. It includes concepts such as: solar shading, thermal mass, ventilative cooling.

Sick Building Syndrome: primary causes

Natural ventilation

Natural ventilation uses natural forces to exchange the air in a building. The driving forces are wind and temperature differences.

Natural ventilation refers to the amount of air that enters a building uncontrolled without the aid of a mechanical device, such as a fan. The force that provides the pressure difference causing the air to flow may be the result of wind action or a temperature difference between the inside and the outside of the building, called stack effect. Stack effect is the pressure difference caused by the variation in temperature and humidity – and therefore density – between the air inside and outside the building. In buildings over the height of 30m, these pressure differences cause summer and winter infiltration and exfiltration, as follows:

• Summer: Infiltration at the top of the building and exfiltration at the bottom
• Winter: Infiltration at the bottom of the building and exfiltration at the top

These opposite directions of air flow through the building balance at a point somewhere near the centre of the building.

In South Africa, where winters are mild, the stack effect is usually small and, in most cases, can be ignored as the amount of infiltration due to wind effect is usually greater than the amount of infiltration caused by stack effect. In residential buildings, air is often supplied through the facade and extract air is removed from selected rooms (often kitchen and bathrooms) through ducts. It can also enter through leakages in the facade. It is important to ensure an efficient air flow path through the building.

Mechanical ventilation

Mechanical ventilation systems use electric fans to direct the airflow in the building. Mechanical ventilation can provide a constant air change rate independently of external weather conditions, but it uses electricity and usually cannot change the ventilation rate as the need changes over the day and year.

Several variations exist. Systems with both supply and extract can be combined with a heat recovery unit, which recovers by reusing the heat of the extracted air that would otherwise be lost.

Up to 90% of the energy can be ‘reused’. Mechanical ventilation requires filters to be changed regularly. Dirty filters are a source of pollution pertaining to the indoor air and reduces indoor air quality. This in turn reduces the performance of the occupants of the building and increases the prevalence of SBS symptoms.

If a mechanical ventilation system with heat recovery is to perform efficiently, the building must be perfectly airtight. If it is not, a substantial part of the ventilation will come from infiltration, which bypasses the heat exchanger. So mechanical ventilation with heat recovery is often not an energy correct solution for existing buildings. Mechanical ventilation systems can be central. Central systems have one central unit, with supply and extract fans. If the system has heat recovery, the heat recovery unit is included in the central unit. Ventilation ducts are installed from the unit to most rooms of the house.

Other ventilation systems do not use ducts; instead, small units are installed in individual rooms of a house. Such a system has the advantage of not requiring space for ducts. Examples would be a bathroom or kitchen extraction systems.

Hybrid ventilation

Hybrid ventilation is a system that combines natural and mechanical ventilation and as such is a relevant solution for new buildings, especially if roof windows are available to facilitate stack effect. Several variations of hybrid ventilation systems exist. Hybrid ventilation can be used to optimise the indoor environment while reducing energy costs. This allows for open windows to be used which is appreciated by most users. It combines the best of both worlds: good winter energy performance with mechanical heat recovery ventilation, and good summer performance with natural ventilation.

The principle of fan-assisted natural ventilation is mainly used in larger commercial buildings where the natural driving forces are inadequate in some periods. A fan is therefore used for assistance.

The principle of stack- and wind-assisted mechanical ventilation is also used mainly in larger commercial buildings, where the ventilation system is designed with ducts to transport the air, and natural driving forces provide most of the airflow with fans used for assistance.

In reality, the need for ventilation changes constantly and the ventilation rate should be increased or decreased dependent on the demand. For example, how many people are present and what are their activity levels?

Deon, I have investigated ventilation contextualised to your question. There are many more aspects to be considered. For example: ventilation can be used to cool an overheated environment, such as laundramats or a boiler room. The amount of people and activity levels in a space are critical to ventilation rate calculations, like a gym. There are of course regulations which stipulate minimum rates as per application, including hospital theatres, bars and restaurants.

Deon, I hope that this helps with your understanding around ventilation and solves your dilemma.

References:

1. ACRA
2. (Bluyssen)
3. ASHRAE
4. World Health Organisation