The energy efficiency in the systems for heating, ventilation and air conditioning became interesting and started to be developed after the energy crisis in 1973. Beside the many rational and efficiency solutions that have been developed, some very exotic ideas were also introduced. Such idea was the seasonal accumulation of the heat in artificial underground reservoirs. These ideas are exotic, because of the non-clarified potential and huge investments, and furthermore there is no information if there are such installations. However, the development of heat pumps allows using the energy of the air and the natural battery – the Earth. The interest in energy efficiency and energy saving ventilation systems follow the tendency in increasing the prices of primary energy sources.

Furthermore, the increase of energy use affects the environment and lead to negative climate changes in the last 20 years. The European Union introduced the program “Europe 2020”, due to the reasons mentioned above. It has the aims:

• Decrease the emissions of greenhouse gases by 20%
• 20% of the energy to be from renewable energy sources
• Increase of the energy efficiency with 20%

The systems for ventilation, heating and air conditioning are extremely huge consumer of energy.

• For heating during the winter
• For cooling during the summer
• For airing (ventilation) during the whole year

According to research of Wigenstad and Grini from 2010, the energy expenses for heating, ventilation and air conditioning in commercial and public buildings are 42% of the total energy expenses, while in domestic buildings the HVAC expenses are 56% of the total energy expenses. (Wigenstad. and. Grini, 2010). A study in the European Union from 2002 showed that the buildings use 40% of the energy in the whole European Union. (ЕPBD 2002, REHVA journal). Following the directive of the European Union, many countries implemented laws and financial stimulus for energy efficient HVAC systems.

• Heat recovery of the energy from the exhaust air should be considered as compulsory action.
• Clients, that have installed heat pumps (АА, СОР> 3.5 – 3.8), receive back 55% of the initial investment (Legge Finanziaria 2008, Art. 1,347 Law No 296 of 27 December 2006)

These measures are still pending in Bulgaria! Despite the lack of strict regulations, we are happy to note that the Bulgarian designers, installers and most importantly – customers, pay more attention recently for energy efficient HVAC systems. The reason is obvious! Energy saving installations for ventilation, air conditioning and heating are ecologically, healthful and economically right decision! Naturally, every investor would like to spend money in the clever way in the process of building a site. The benefits of good thermal insulation and solid widows are indisputable and legally regulated. Each building with low energy consumption begins to look like a “thermos” in which the coffee is hot and after 12 hours. The only disadvantage is that we live in this “thermos”. A human can live 3 weeks without food, 3 days without water and 3 minutes without air! Good microclimate, temperature, humidity and fresh air are prerequisites for efficiency at work, low illness and incidence. The economic effect of these prerequisites is clear. I would like to discuss only the systems with heat recovery due to a few reasons. First, because the heat pump installations are well researched and promoted by world manufacturers. Second, because the energy costs for ventilation, often exceed those for the heating and cooling in modern buildings. Our company has more than 20 years of experience in developing mechanical heat recovery ventilation is the third reason. The new buildings made in the last decade cannot be ventilated by opening of a widow. Mechanical ventilation is required and heat recovery is a wise decision in my opinion. Investment for mechanical heat recovery ventilation is higher for sure, but the return of this investment is only 1.5 – 2 years. After that period the system continues saving you money. There are few factors that influence this return of investment period:

• Climate zone
• Working time  (hours/yearly)
• Price of energy
• Price of equipment
• Maintenance costs
• Interest at the credit (if the building installations are made with credit)
• Financial stimulus for energy saving (efficiency)
• Costs for emissions
• The market value of the site, as function of the extras included

The graph below shows the idea for different installations for one project, according to their initial investment and energy efficiency.

— E – 1 – 0% heat recovery
— E – 2 – 50% heat recovery
— E – 3 – 60% heat recovery
— E – 4 – 70% heat recovery
— E – 5 – 80% heat recovery

The mark area with white and black shows the value of loss if an investor chooses improper installations. Often the initial investment is a priority when making the decision and choosing one or another system. That is why, specialists and engineers should provide more information and clearness of different systems and their life cycle period. The systems for heat recovery in ventilation systems can cost 0!  There is perception, even in some scientists, that the effect of heat recovery is very low. Even though that the working hours with temperatures above 25 degrees are not so much in Bulgaria, I would like to draw the attention in the calculation of heating and cooling centers. If the designer calculates the cooling or heating center with and without mechanical heat recovery ventilation, he will find out that the needed cooling and heating capacity is very different. Thus the designer can choose lower capacity chiller/heat pump and a lower capacity boiler. The difference in the initial investment of the lower capacity chiller will return the investment in the heat recovery ventilation. There is a tendency in the recent years to increase the efficiency in the heat recovery systems. This is due to the rise of the price for primary energy and the striving of the European Union to cover the parameters in the program “Europe 2020”. The change in the EUROVENT classification and EN 308 confirms my statements above. Classification of the energy efficiency of Air Handling Units.

The requirements for energy saving were varied according to the air volume in 2008. Unfortunately, sometimes the marketing and sales techniques overrule the professionalism and today some companies show efficiency above 95%. However, the new line of mechanical heat recovery ventilation TANGRA EVB HiE covers the highest classes of EN 308 and EUROVENT. Three or four years ago, our heat recovery ventilation has an efficiency between 50 – 60 %. The new line heat recovery ventilation reaches real efficiency of above 80% with equal mass flows and without condensation (EN308). We export and sale more and more successfully these high efficiency heat recovery ventilation systems thanks to the high quality and competitive price. TANGRA export mechanical heat recovery ventilation in more than 10 countries in Europe.

Dipl. Eng. July Armianov General Manager „TANGRA-AV” ltd.