Ventilation Systems

Cost-efficient ventilation systems are vital in modern buildings leading to occupants being more comfortable and as a result more productive. This is particularly important when you add the fact that we spend about 90% of our time indoors to the raging debate currently surrounding indoor air quality - in particular topics such as passive smoking, Legionnaires disease and sick building syndrome.

But is it an economic argument too. In the workplace, where salaries consume about 80% of the costs of office buildings, the 3-10% loss in employee productivity believed to be caused by poor air quality is quite significant. In fact, one study has revealed that a drop in employee performance of just 2% is likely to exceed the cost of providing good indoor air quality.

This low productivity is demonstrated by low employee morale and high rates of sick leave as well as employee drowsiness; headaches and nausea; poor concentration; dry itchy skin, irritated eyes, noses and throats; excessive colds and allergies; and constant grumbling about the humidity and/or temperature.

The effects of temperature have, in fact, been quite well studied. Office temperatures above 24°C have been found to result in a reduction in employee concentration of between 30 to 50%. In factories, where loss of concentration can be potentially life threatening, accidents significantly increase at temperatures greater than 25°C.

But temperature is just one component of IAQ, which is also influenced by humidity pollutants and air movement. Some of the reasons for poor IAQ therefore include inadequate HVAC design or maintenance, insufficient amounts of fresh air and relative humidities below 40%. As the pollutants include volatile organic compounds, ventilating air should be pre-conditioned before it is introduced to a building - exploding the old myth that the answer to pollution is dilution' - which is part of the reason that the HVAC system design is important.

One significant product currently on the market that proves this point is the Mitsubishi Lossnay unit that has sold over a million world-wide in the last 20 years, largely due to the products' simplicity and efficiency. Specifically Lossnay (which means 'no loss' in Japanese) breaks the assumption in end-users minds that effective ventilation systems have to be inextricably linked to wasting energy and increasing costs.

ventilation systems

ventilation systems

The units reduce overall energy costs by extracting stale air and then recovering the heating or cooling energy to either warm or cool in-coming fresh air This is achieved using a cross flow total heat exchanger made of specially treated paper plates and fins. Inside every Lossnay unit the fresh air and exhaust air passages are completely separate, allowing the fresh air to be preconditioned to the temperature and humidity levels of the room air without mixing with the exhaust air.

The operating principle is based on the heat transfer properties and moisture permeability of the treated paper. You only have to roll a piece of ordinary paper into a tube, wrap your hand around it and blow down the tube to see how effective paper is at transferring both sensible and latent heat. This is despite the fact that paper is generally regarded as heat insulating material. In fact, in gas to gas exchanges, the thermal conductivity of paper is comparable to copper and aluminium, which accounts for the sensible heat exchange. The latent heat exchange occurs as a result of osmosis, created by the paper's carefully controlled porosity.

In fact the eight commercial units in Mitsubishi Electric's Lossnay range, which can be installed independently or used in conjunction with City Multi and Mr Sim products are so efficient that they recover up to 70% of heat from stale air. This reduces the energy costs of conventional air conditioning equipment for a given fresh air delivery rate by up to 30% and can also reduce the cost of the initial installation by between 5% and 10%.

Other Lossnay benefits include automatically humidifying or dehumidifying in-coming air to match the room requirements and the fact that only fans are used to simultaneously expel stale air and introduce fresh air, enabling healthy ventilation, even in an otherwise air-tight room. Additionally, as Lossnay is responsible for a large reduction in the ventilation load it enables specifiers to select cooling or heating plant with a 20-30% smaller capacity.

In contrast, past attempts to control air quality and keep costs down led to complex solutions with laborious installation work, resulting in systems that were hard to manage and control.

For example, on some air conditioning systems, air renewal involves cyclic cooling and heating of the incoming airflow, without enabling the heat and humidity of the air to be used. Consequently, as the renewed air does not undergo heat or humidity treatment the air conditioner has to work at full power, potentially increasing the cost.


The cost of maintaining constant thermal conditions inside a room can be quite significant. As the table shows, the enthalpic difference (or difference in the amount of calories) between the air outside and inside a room is about 3 kcal/kg in summer and 9 kcal/kg in winter. To put these figures in a meaningful context, renewing the air in a moderately filled restaurant containing approximately 40 people would require an additional 3,750 W in summer and 11,300 W in winter This is in addition to the energy needed to compensate for normal input and losses through structures.













Corby Refrigeration, Gordon House, Dale Street, Corby, Northamptonshire, NN17 2BQ UK
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