The same solar system with different uses: Over a. Drainback systems: empty and safe

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1 Drainback systems: empty and safe Larger systems may also be installed using. Photo: ESE Modern thermal systems are reaching ever-higher temperatures. Although this is desirable on the one hand, because they can work more efficiently, it can lead to problems on the other if the system goes into accidental stagnation. Drainback systems provide a simple protection method in that they empty out the heat transfer medium from the collectors. Here is an overview of the systems and the ways they work. The Drainmaster is installed directly below the collectors. Photo: Biotech The same system with different uses: Over a 12 month period the company Viridian Solar Ltd had the energy use of six families in the county of Suffolk and in the city of Sheffield independently tested. The result: The same systems by the British supplier lowered conventional energy use by varying amounts. While one family only got a quarter of its hot water use heated by the system, the best household managed 70 %. Although the families treated their systems very differently, the families still had one thing in common: the systems on their roofs were all systems. The special feature here: If the system stops, the heat transfer flows out of the loop and into a spe- cial container it thus cannot evaporate in the collector or freeze. Drainback systems can thus use water alone as a heat transfer. And a further advantage: systems do not need an air bleeding valve, check valves, safety valves or an expansion tank. This simplifies the systems and makes them easier to install. Drainback is an easy way to protect systems against over and frost damage. Wrongly installed s can prevent a complete emptying of the collector and s, though. The collecting main must have a constant and minor downward angle of a few degrees. This can be hard to achieve in some cases, for example if the number of collectors desired by the customer cannot all be installed along- 48

2 side oneanother on the roof because of dormers. The German supplier Rotex Heating Systems GmbH solves the problem by splitting up the return route and connecting up each collector area from below with a constantly-angled. The supply s attached from above are joined together and run to the via a common along the roof crown. Containers take up collector s Despite the frost-protection mechanism of drain back systems, most suppliers work with a water and glycol mix in their systems to be on the safe side (see table on page 52). They thus protect their systems from damage should the installation work not have been carried out correctly. An example is Conergy GmbH from Switzerland. Their Sunrise 2000 is a system in which the from the collectors runs into a container built into. Conergy have given this container the name BackBox. It already contains the heat transfer when it leaves the factory and is thus all ready to go. With the first ray of sunshine our system starts up automatically, promises their company advertising. Thanks to this arrangement the installer saves himself the task of filling and bleeding the system and of setting the controls. It s an advantage shared with other systems. As soon as the storage has filled up with heat the s stops the system and the runs into the BackBox. The BackBox is also available as a separate unit. According to Conergy it may be combined with all conventional boilers and s, regardless of whether these have integrated heat s or external plate s. In the Streamline hot water system by the Australian world market leader Solahart Industries Pty Ltd, a container is integrated into the in a similar way to that of Conergy. It forms a compact unit together with a set of s, a heat and a controller. Solahart s external unit is called Powerbak. It can be combined with any and can thus also be used in systems. Powerbak brings together the hot water and collector, the heat, the control and display unit and the container. The Dynasol unit by the Belgian company European Solar Engineering SA (ESE), the Clearline-Station by Viridian Solar and the units by the Dutch company Itho Images b.v., also house further components aside from the container itself. These can include the, a shutoff valve, a controller, temperature sensors and connections with which they may readily be hooked up to the storage tank. The system makes it possible to separate the collector and tank, as long as the third component, the unit, is situated lower than the collector, says Itho, describing an advantage of its system in a product description. The tank can thus be placed anywhere inside the building. This degree of freedom in placing the collector and tank makes the integration of a system possible for almost every house, says the company, independently of free roof or the location of the central unit. A further advantage of boxes: They can be linked together if the systems are larger. One disadvantage, though: The s have to be powerful enough to deal with the difference in height between the container and the collector. Such s are not normally available as standard, are thus expensive, and are sometimes also louder than conventional rotary s.

3 The craftsmen have to work carefully when installing a water-filled system. The piping must be at a constant downward angle so that frost damage cannot occur. Photo: Rotex Drainback boxes, as used by Solahart, may be joined one after the other to serve larger systems. Photo: Solahart Drainback boxes contain not just the container but also the, a shut-off valve, the controller, temperature sensors and connections with which they may readily be hooked up to the. Photo: Itho Drainback capacity in the heat : Apart from boxes with containers, there is a common variation in which loop is stored within the heat of the when the system is not in operation. Diagram: Wagner & Co. The Austrian biomass boiler manufacturer Biotech Energietechnik GmbH supplies an alternative product, the Drainmaster, which doesn t have this problem because it is mounted directly on the collector. The Drainmaster only empties the collector field. Due to its position directly below the collectors, the system can be used with normal s. A further advantage: Conventional systems may be converted to systems at a later date. When the circulation switches on, it fills the collector field with from the reserves in the Drainmaster, which in turn takes up the air from the collectors. When the switches off, the can once again collect in the Drainmaster. As with the Biotech collectors, it can be mounted in the roof covering, on the roof or on facades. Biotech supplies the Drainmaster as an optional accessory for its systems. 50

4 The Dutch company Zen supplies variations with a container in the or in an external vessel. Photo: Zen Heat s in the act as the container The German companies Wagner & Co Solartechnik GmbH and Vaillant GmbH & Co. KG, as well as AWB CV-ketels b.v. from the Netherlands and Saunier Duval from France, which both belong to the Vaillant Group, manage without boxes altogether. In their systems an overdimensioned heat in the takes up the when the system is not running. Wagner has developed the Secusol system as a compact unit, which is suitable wherever there is little available. In the system is mainly used in single-family homes with a low hot water demand, such as in terraced housing, for example. The volume of in the thin s and in the collector field of the Vaillant Aurostep system is low compared to the thick coil in the. Because of this, the level of the only goes down a limited amount when the collector is on. Air forced out of the s and collector field collects in the upper portion of the coil. As the system heats up the and the air expand somewhat and the pressure of the air enclosed in the system increases slightly. The enclosed bubble of air in the system takes on the function of a compensating unit. The pressure is necessary, says Vaillant, and must not be bled off. For this reason the system must not have any bleeding valves installed. Collectors empty into the The German manufacturers Con GmbH of Frankfurt and Rotex Heating Systems GmbH require neither a container nor an over-dimensioned heat in the as the volume. The itself acts as the collection container. Because they are open systems, which are not under pressure, it is possible to use vessels made of plastic here. Both systems use water alone as the heat transfer. In the Rotex system, a corrugated stainless steel heat, fully covered by stored water in the upper part of the tank, heats the drinking water. A stainless steel heat lying below can be used to both store heat from the network and transfer heat to the network from heat generated by the sun. If the controller turns off the, air flows into the system via a ventilation hole and the system empties itself. Thanks to a special construction of its, Con doesn t heat up the entire contents of the tank, but feeds the heat directly to the secondary heater as required. The heated loop water is thus fed directly into the hot-water standby unit in the summer, while in winter it flows to the loop via the outer jacket 51

5 Company Astersa SA, Spain Atmos Heating Systems, Great Britain AWB CV-ketels b.v., The Netherlands Biotech Energietechnik Austria Conergy Switzerland Con Product name Max. collector circuit length [m] Max. height difference [m] Tank volume [litres] Collector surface area [m²] Absorber type or 2.4 harp-type absorber Mono Helio Set 150 Biotech Drainmaster BDM Sunrise 2000 CD Solar, Italy ESFVD 200 / 300 European Solar Engineering SA, Belgium Itho Images b.v., The Netherlands Rotex Heating Systems Saunier Duval, France Solahart Industries Pty Ltd, Australia 20 (in-system) and 40 4 (8.5 optional) optional 2 optional 2 depending on number of collectors / / / / 8 Solar Pur to 10.5 Dynasol and Domosol DBU 1 / DBU 2-4 Rotex Solaris Helio Set 150 / / / 2.60 / 4.48 / / 300 / 400 / 500 / / 4.64 / 6.96 / / / 4.6 / 6.9 / 9.2 (A, D, SK), harp-type absorber (I, ES) 30 to bis (in-system) and / / 5.01 Stream-line up to 6 copper array, copper sheet, blue selective surface Power-pak 10 kw up to 1,200 up to 14.9 full-surface absorber Drainback volumes drain back incorporated within storage tank, seperate drain back tank has a volume of 10 litres Drainmaster already filled in (factorymade), integrated back box as return vessel unpressurised plastic tank or extra tank unit, pre-filled unpressurised plastic tank vessel with 16 litres 50 litre tank Special properties Heat transfer Pump Type of use Internet hot water water stainless steel storage unit with preinstalled and pre-wired control, antifreeze medium factory-filled Drainmaster directly mounted underneath collectors, wiring to tank variable enamelled with integrated drain back reservoir and premounted station as well as controller piping made of metal-plasticcompound tank is also vessel, and control are integrated in the tank, vacuum break valve for piping on the top side of collector copper or polyamide piping water hot water special centrifugal rotary with speed control volumetric 4 hot water water tank is simultaneously reservoir stainless steel storage unit with preinstalled and pre-wired control, antifreeze medium factory-filled vessel, and controller are integrated inside the tank Powerpak is combinable with any tank, hot water and/ or support water circultaing plus pressureincrease hot water Salmson HXL63-15P additional booster hot water 52

6 Vaillant GmbH & Co. KG, Viridian Solar Ltd, Great Britain Wagner & Co Solartechnik Zen International, The Netherlands Aurostep VSL S 150 / S (in- system) and / / 5.01 Clearline / 200 / 250 / 300 Secusol / / / (only Italy) Zen Renewables SDB 90 / 150 / 200 / 250 / / 250 / 250 / / 150 / 200 / 250 / / 2 / 3 / 4.5 / / 2.6 / 4.4 / / 4.2 / 5.6 / 7 / 8.4 unit or external vessel (standard: 10 / 20 / 30 litres) stainless steel storage unit with pre-installed and pre-wired control, antifreeze medium factoryfilled storage unit with control,, safety system (except 350-2) hot water central circulation rotary hot water With optional separate insulated tank 15 m; 2 Drainmaster mounted directly underneath collector; 3 Drainmaster available until 12 Biotech collectors; 4 with separate back box; 5 with an accessory third 16 m; 6 bigger collector areas possible; 7 a booster can increase the maximum collector circuit lenght to 60 m; 8 use of a booster raises the maximum unit height to 18 m; 9 a booster can increase the maximum collector circuit lenght to 40 m; 10 use of a booster raises the maximum unit height to 16 m; 11 higher with external vessel of the powerful middle heat and in the opposite direction to that flow. Because the Solar Pur system operates without a heat and can thus give up its heat without transfer losses, it achieves between 10 and 30 % higher yields according to Con. The company developed the system in a four-year development project at the turn of the millennium. During the course of this it also designed plans for systems with active frost protection, elastic stretchable s and s with integrated expansion bodies. Con opted for the solution because this had been shown to be less risky and closer to the market s wishes. Y Joachim Berner Technical overview of systems Source: manufacturers information, own research; date: September 2008 THE FUTURE ABSORBER is made from aluminium We weld with ultrasound all metallic compounds copper/copper alu/copper alu/alu Ultrasonics Steckmann GmbH Hauptstraße Grävenwiesbach Telefon: Fax: mail@ultrasonics.de Internet: