Good air at home, a necessity
Many of us spend at least half of the time at home in our houses and apartments. All air is polluted to some degree. Normally we think about car exhaust gases and various other types of emissions when we discuss these things. Untreated air coming into our homes will carry any number of pollutants with it.
As our homes are well insulated and often with double or triple-glazing windows, the air tends to linger. It’s an unfortunate fact, but the better our home is insulated the more likely it is that the air quality will be poor.
Good air at home not only means increased well-being, but also that we perform better.
For children, good air is even more important in order to avoid Asthma and allergies, diseases that are being established early and which according to many researches largely depend on the indoor environment.
Ventilation solutions for our homes;
The purpose of ventilation is to enable us to breath clean air by removing the stale, polluted air from our homes whilst replacing it with good quality air.
There are three types of technical system solutions for ventilation. Within these are of course variants but the main types are:
- Natural ventilation
- Fan controlled extract air system
- Balanced ventilation system [which consists of supply as well as extract air fans complete with recovery unit as rotary or counter-flow unit]
Natural ventilation system
The principle for natural ventilation is simple. The warm air indoor will rise and disappear via ducts, which creates a negative pressure in the building. Due to the negative pressure, new air is being sucked in from the outside, the new air comes via gaps and openings in the house or an apartment. No fans or other mechanical devices are needed, which sounds like the ideal ventilation for all types of dwellings. A simple thing like insulating tape in the windows can ruin a complete natural ventilation system and make the ventilation insufficient. The larger temperature difference between indoor and outdoor air, the larger volumes of air being replaced. In the summer when the difference is small or none, there will be no ventilation. Natural ventilation is therefore always complemented by opening windows, especially during the warm part of the year when the natural driving forces are non-existent.
Early natural ventilation systems worked well enough as houses were not well insulated, and rooms tended to be larger. The chimney was always warm as it was necessary to have a fire lit to provide hot water and a means to cook.
Even a natural ventilation system that works from a ventilation point of view involves some undesired effects. If the airflows are sufficient for creating good air indoors you will waste energy as the warmed air will go straight out and its energy loss. If you solve this by reducing the airflow, the indoor environment becomes unhealthy as the air quality deteriorates.
Another problem with natural ventilation is that one cannot control the ventilation, we are at the mercy of the elements. The air will not be cleaned as you can’t out a filter over every source of air inlet. Filtering air is an obvious solution when we live in cities or where there are known pollutants in the atmosphere, or if we live near busy roads. But consideration should also be given to filtering air in areas where it is perceived to be unpolluted, as a good quality filter can remove pollens that can often trigger an allergic reaction.
All air leaving the building will be replaced with unheated air from the outside. The fresh air must be once again heated, which costs energy. The incoming air fresh air can also cause draught, a common reason for putting insulation tape around windows and doors. Draught is not a problem during the warm part of the year but can become a nuisance during the winter when the incoming fresh air has a temperature below 0°C.
Fan controlled extract air system
Mechanical extract is when we use fans to control the airflow rate in the home or an apartment. The fans extract the air from the dwelling by means of a motor and impeller mounted in some kind of casing. The air is normally extracted from the kitchen, bathroom and laundry room. These are the rooms where moisture and unwanted odors are most likely to occur. In the same way as, natural ventilation happens the air is replaced via gaps under doors, around the window frames and if fitted, fresh air intake grilles.
It is important not to remove the air via bedrooms and the living room as the air will flow in the wrong direction with the consequence that smell of cooking and moisture will spread through the dwelling.
Fan controlled extract systems are popular as it is an inexpensive and easy to install method of ventilating the home or an apartment. However, such system has the same disadvantage as natural ventilation in that the incoming fresh air is untreated and will be cold in the winter and is almost certain to be contaminated with pollutants. Therefore, it is common for the fresh air grilles valves to be closed in the winter and any gaps under doors or around window frames to be sealed. The result is less cold draught, but the air quality suffers with the reduced volume. The result is fewer cold draughts, but the air quality suffers with the reduced volume of air able to get in. the air stays longer in the room and we breathe the same air over and over again. Nowadays grilles can be supplied with filters that take care of the coarse pollutants. By proper sizing and placing of diffusers, draughts can be avoided.
Balanced ventilation system
The most complete form of ventilation system is said to be the so-called balanced system. Fans control both supply and exhaust air, which means that one has full control over the volume of fresh air, which is not the case in the other systems. In fairly well insulated houses one can claim that practically all supply air comes through the supply air diffusers, as the system is not based on negative pressure. It also means that it is easy to clean the air. You put the filters at the air intake and in return air grilles.
Balanced systems are nothing new but have struggled to find a demand for use in our homes and apartments. On the downside the system is more expensive to purchase and install than the other systems, but in its favor is the opportunity for energy savings and creating a more comfortable environment. Today the systems are both effective and quiet and there is lots of research showing that if you want an installation with both low energy consumption and good indoor climate you need a balanced system. Low usage of energy implies heat recovery and energy efficient products like fans, filters and heat exchangers.
A good balanced system is both stable and flexible. Stability means that the system should function as intended almost regardless of what is being done in the house or apartment. Flexibility means that one should be able to control the ventilation on demand, more ventilation is needed when many people are in the house than when the house is empty.
Such ventilation control by demand becomes more and more common and in combination with heat recovery, the energy requirement decreases, and the operating costs go down.
A balanced system with heat recovery is the most ideal system. Instead of sending the used warmed air straight out, it is passed through a heat recovery unit where the exhaust air heats up the cold fresh air intake in. In recent systems, heat recovery can vary between rotary recovery system (up to 85% recovery in ideal condition), counter-flow recovery system (>90% recovery in ideal condition), hygroscopic or descant wheels for heat and enthalpic recovery and lastly enthalpic counter-flow exchanger for heat and humidity recovery.
Balanced systems can vary for a small student apartment of 35m2 to large villa of 1000m2. Depending on geographical area of installation the recovery can be rotary or counter-flow. Typical small units are used in combination as cooker-hoods. When using the ventilation unit in cooker-hood mode, the air is completely bypassed in order not to build fat particles on the recovery system. Recovery units can be wall or ceiling mounted depending on the size and air volume necessary. In the case of multi-residential installation, smaller air handling units with rotary or counter-flow recovery is used. Then after each apartment has a controlled ventilation system through a VAV-Box which integrates a set of variable air volume for supply and extract with silencer section. These units have integrated controls with or without communication to give the possibility to be managed through smart home control system.
It is essential for the balanced system to be properly designed and install to function adequately, for as any incorrect duct or air inlet/outlet sizing will add to the system pressure. Increasing the system pressure unnecessarily will result in bad ventilation and sound problems for the resident.
Good ventilation system will not only have proper sizing on the ventilation unit, but also on all components of the system in order to properly balance the airflows with low pressure system designed to meet the occupants needs.
In a well-designed system, the occupants will not know when the system is running and at which level and only feel comfortable in their daily activity.
Ref: Svensk Ventilation hand book “shortness of breath”