© Photo | Boesch

Prize-winning low-energy housing complex

Energy-effi­cient air-condi­tioning tech­nology in Switzer­land

Energy-effi­cient air-condi­tioning tech­nology with modern Green­Tech EC fans

Last year, the Solar City housing complex in the wine-growing region of Satigny was awarded the Swiss Solar Prize 2011 in the cate­gory “Energy Systems for Renew­able Ener­gies” for its eco-friendly energy and heat gener­a­tion. 80% of the energy needed is gener­ated by the complex’s own solar system. An impor­tant basis for the effi­cient us of regen­er­a­tive primary energy is provided by the modern air-condi­tioning equip­ment employed for venti­lating and heating the complex. When the windows are closed, it provides for a require­ment-orien­tated air exchange and optimum air condi­tioning. The high-perfor­mance and yet energy-effi­cient fans with Green­Tech EC tech­nology supplied by ebm-papst which are employed in the HVAC systems make a major contri­bu­tion to this.

The Solar City complex, which was completed in 2010, consists of four large build­ings containing a total of 78 housing units and a large under­ground garage on two floors. The joint project between the company ERTE Ingénieurs Conseils SA from Geneva and the vintner family Bonnet from Satigny was constructed to the Minergie S stan­dard. Minergie is the highest energy stan­dard in Switzer­land for low-energy housing and is roughly compa­rable with the German stan­dards for energy-saving houses KW40 (for new build­ings) and KW60 (for refur­bishing older build­ings).

With the power of the sun against frost

Around 1,160 m² of unglazed, walk­able solar collec­tors have been fitted to the roofs of the resi­den­tial build­ings. These have been designed to generate energy even in unfavourable condi­tions

As the name suggests, the Solar City social housing project relies heavily on the power of the sun. Around 1,160 m² of unglazed, walk­able solar collec­tors have been fitted to the roofs of the resi­den­tial build­ings. These have been designed so that they are still able to generate energy when condi­tions are less than optimal, even when it is raining, snowing or in moon­light. That enables the thermal solar system to generate some 80% of the total heat energy required. Green elec­tricity from the grid accounts for the remaining 20%. Solar City employs an inge­nious combi­na­tion of direct hot water gener­a­tion and heat pumps without addi­tional expen­sive seasonal reser­voirs or geot­hermal energy gener­a­tion with under­ground probes. This was an impor­tant argu­ment for the nomi­na­tion for the Solar Prize.

The effi­ciency of the concept has now been proven in prac­tice. At the start of 2012, during the almost Siberian cold spell, it was really put to the test. With temper­a­tures aver­aging -11 °C and 15 cm of snow on the solar collec­tors, it was still able to heat the complex without diffi­culty. The 55 °C required in the boilers was achieved. The temper­a­tures inside the apart­ments was a comfort­able 21 to 22 °C. The resi­dents had ample supplies of hot tap water. The addi­tional elec­tric heating elements which had been installed in the boilers for use in worst-case condi­tions were not employed even once. Despite the frosty temper­a­tures outside, none of the resi­dents had to freeze.

Venti­la­tion concept saves energy and enhances living comfort

The RLT units of the type Optima ME from the company Bösch are compliant with the latest find­ings in the field of energy and hygiene, and satisfy all rele­vant stan­dards which are applic­able today for minimum energy equip­ment

Such an energy concept cannot work without controlled living room venti­la­tion. A partially centralised system was chosen for the venti­la­tion and air condi­tioning of the apart­ments. Here, the four build­ings were split into ten sections, all of which are iden­tical in their construc­tion, and supply up to eight housing units. Each section comprises a unit for controlled living room venti­la­tion and heating, a heat pump and a sepa­rate hot water reser­voir. The energy consump­tion is indi­vid­u­ally recorded for each housing unit. The recorded oper­ating data for the complete complex are sent by internet to the Univer­sity of Fribourg for eval­u­a­tion.
The centrally installed RLT units of the type Optima ME, supplied by the company Bösch (see box text 1) are respon­sible for a comfort­able living climate in each section. These were designed specially to comply with the Minergie stan­dard. The new line of units (see Fig. 3) with air perfor­mance of 400 to 7,000 m³/h are compliant with the latest find­ings in the field of energy and hygiene, and satisfy all rele­vant stan­dards which are applic­able today for minimum energy equip­ment. The design of the air condi­tioning equip­ment plays a deci­sive role here.

Energy-effi­cient centrifugal fans

Back­ward curved fans with Green­Tech EC tech­nology provide for the neces­sary air flow in the centralised air-condi­tioning units

Large-area, humidity-resis­tant fine dust filters made out of pleated glass fibre mate­rial of class F7 pursuant to EN 779 with a protec­tion rating of more than 60% provide for a high level of air clean­li­ness and guar­antee a healthy room climate even when the outside air is polluted with fine partic­u­late matter. The ultra-effi­cient heat regen­er­a­tion system (the residual heat coef­fi­cient ɸ is greater than 80%) guar­an­tees an optimal re-use of the heat in the exhaust air. The heating of the fresh air, which is needed at very low outside air temper­a­tures, is achieved with a PWW (pump/warm water) register from the heat pump. To generate the neces­sary venti­la­tion and air extrac­tion flow, two centrifugal fans are used in each of the units. These are highly energy-effi­cient and are regu­lated extremely econom­i­cally (see Fig. 4). They are taken from the product range of motor and fan specialist ebm-papst and are specially designed for use in venti­la­tion and air-condi­tioning tech­nology. Different versions ensure that the optimum fan solu­tion can be found for every air-condi­tioning unit. For example, in the central air-condi­tioning systems in Solar City, Bösch employs centrifugal fans of size K3G280 with back­ward curved blades. These fans work chiefly by suction, do not require a scroll housing and have a high level of hydraulic effi­ciency. Further­more, the Green­Tech EC tech­nology also means a whole lot more other advan­tages.

Freely adjustable controls and pleas­antly quiet

Because the EC motors work so effi­ciently, they consume substan­tially less energy that conven­tional AC drives

The EC motors that power the fans feature an inte­grated elec­tronic control system that allows the speed of the fan to be adapted precisely to what is actu­ally required. Require­ment-orien­tated oper­a­tion can be controlled either with an analogue 0-10 V signal or via a digital RS485 inter­face. Because the motors also work with great effi­ciency, they consume substan­tially less energy that conven­tional AC drives, not just at full load but also in part-load oper­a­tion.

At the same time, they create prac­ti­cally no motor noise. In contrast, asyn­chro­nous motors driven by a frequency inverter, partic­u­larly under partial load, produce reso­nance noise that results in the typical unpleasant motor hum. This would certainly not provide a pleasant living envi­ron­ment. The resi­dents of Solar City have nothing to fear. The air-condi­tioning units are equipped with fans powered by pleas­antly quiet Green­Tech EC tech­nology. These are prac­ti­cally inaudible in the apart­ments and on the stairs.

Noise emis­sions of AC and EC motors in compar­ison

Another advan­tage of these fans is their compact design. The elec­tron­i­cally commu­tated external rotor motor is directly inte­grated into the impeller, which reduces the instal­la­tion dimen­sions. A belt drive between the motor and the fan, which is commonly used other­wise, is not neces­sary. This reduces not only the required instal­la­tion volume – always desir­able for the air-condi­tioning units made by Bösch – but also the asso­ci­ated instal­la­tion complexity. At the same time, fewer parts are required which are subject to wear. This keeps service costs low over the long term and thus saves money for the oper­ator. More­over, the design of the fans permits hygienic main­te­nance.

About Walter Bösch GmbH
Walter Bösch GmbH & Co KG is based at Lustenau in the Austrian state of Vorarl­berg and has been in exis­tence for more than 80 years. Started as a one-man oper­a­tion, the company has grown into a medium-size organ­i­sa­tion with around 650 employee. It is one of Austria’s leading compa­nies in the fields of heating, air-condi­tioning and cleaning tech­nology. Its air condi­tioning and venti­la­tion systems are custom-built to cover the dehu­mid­i­fi­ca­tion and venti­la­tion require­ments of a small hotel bath­room or the air condi­tioning require­ments of indus­trial produc­tion halls and clean rooms. They can be installed in the base­ment or weath­er­proof versions can be fitted on the roof. Intel­li­gent control solu­tions and complete systems with inte­grated heating and hot-water produc­tion bear witness to the syner­gies between the different company divi­sions.

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