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With rainwater 80% of the energy to cool buildings and costs for water softeners can be saved

In the current situation of global warming, it is becoming increasingly important to provide economic cooling systems using resource-saving technologies.

The adiabatic cooling plays a crucial role. Through the evaporation of water, a preexisting airflow is cooled very efficiently and with low energy consumption. The adiabatic cooling, or colloquially also evaporative cooling, is THE first form of air cooling and almost forms the beginnings of climate technology.

Functionality

The warm outdoor air is sucked and pre-cooled by the heat exchanger. The air is then supplied to the room and there it is heated by people and equipment and humidified some more. Subsequently, the used exhaust air is drawn from the room. Then the so-called "adiabatic cooling" follows, which is nothing else than the humidification of the exhaust air to the saturation point, until it has a humidity of almost 100%. This has the consequence that the exhaust air gives off the amount of energy to the water, which is necessary in order to vaporize the appropriate amount of water. The result is a cooler humid air, which now takes - with the aid of the previously mentioned heat exchanger - energy of outside air and thus cools it. The exhaust air itself is heated again and blown through an external grid at the house front in a certain amount into the environment. The functionality of the adiabatic cooling is shown schematically in figure 1.

The adiabatic cooling can be exemplified in h, x-diagram (figure 2).

The exhaust air leaving the room, is cooled due to evaporation from 25°C and a relative humidity of 50% to 18°C and an air humidity with almost a full saturation of 98%. (Blue mark). This high air humidity, however, can only be reached with certain humidification technologies, such as high-pressure humidifiers. In conventional contact humidifiers, an air humidity of about 85% - 92% is reached.

The yellow mark shows the alteration of the air supplied to the room (outside air) and the alteration of the cooled air by the evaporation, which will be discharged to the outside (exhaust air). The outside air is cooled in the heat exchanger from 35°C to 23°C and reaches an air humidity of 61%. The air now enters the room pleasantly cool and damp. In the heat exchanger the cooled exhaust airflow absorbs the heat of the outside air and is discharged to the outside when warm (exhaust air: 30°C, 47% rel. humidity).

Operating costs and savings potential

This type of building cooling has high energy saving possibilities, which of course you will also notice on the cost side. That way you can compare the power consumption of an adiabatic cooling system and the power consumption of a system with compression refrigeration with conventional air conditioning.

To transform water into steam (in the technical jargon: evaporation heat) 2.300 kJ per kg water is needed. When the water r now evaporates for one hour, the ambient air is cooled with a cooling capacity of 640 W.

Example:

 Adiabatic cooling      Air conditioning system
Power consumption      0,186 kW1 kW
Cooling capacity3,8 kW3,8 kW
Electricity costs€ 0,37€ 2,00

 

A classic air conditioning system with a generated cooling capacity of 3.8 kW consumes 1 kW electrical power. With a current electricity price of 25ct / kWh and eight operating hours of the system per day, this will cost € 2.

In comparison, the adiabatic cooling:

The energy demand of the high pressure pump for atomization is approximately 25 W per kg water. With my efficiency of 80% and 7.43 liters of evaporated waterwhich is required for a comparable cooling capacity (3.8 kW) of an air conditioning system, the atomization consumes 185.75 W. The adiabatic cooling minimizes the costs to €0.37 when used for eight hours.

The bottom line corresponds to the adiabatic cooling with savings of over 80%. The use of an adiabatic cooling system saves a lot of primary energy and is thus an essential contribution to the reduction of CO2. In addition, there is a high potential for cost savings.

Water consumption

In the presented example, 3.5 g of water per m³ of air are supplied to cool the 25°C warm air with 50% air humidity (11.5 g water content) to 18°C with 98% hair umidity (15 g water content). As in the example, the outside air can then be cooled over the heat exchanger from 35° to 23°.

For the air cooling of a room with 3000 m³, x 3.5 g = 10.5 kg of water would be needed. This would represent a cooling capacity of 8.4 kW.

For a nominal volume flow of 1500 m³ / h an air exchange of 0.5 / h results in the following water demand per day: 1500 m³ / hx 3.5 g / m³h x 8 h = 42 l

At 250 working days / year which would theoretically without further heat loss 10.5 m³ / year.

Climate protection

Nowadays, efficient construction is a very important aspect in the context of global warming, as well as the related climate protection. Currently crucial here is the Energy Saving Ordinance (EnEV) 2016. This provides, among other things, energy efficiency of newly constructed buildings. Opposite the already demanding requirements of the EnEV 2014, the annual primary energy consumption must be reduced by another 25% by appropriate structural or technical measures.

This requirement ideally corresponds to the use of evaporative cooling in cooling processes of air conditioning technology. Another climate-friendly aspect besides low power consumption, is the operation without damaging refrigerants, which are used in most air conditioners for cooling. Many refrigerants have an ozone-depleting effect and are therefore committed, due to the chemical climate protection regulation, to a very precise and elaborate sealing with a regular analysis.

Rainwater instead of drinking water

Particularly rainwater is a good resource for the adiabatic cooling. Using rainwater has many advantages, which both have cost saving, as well as eco-friendly effects. Firstly, the demand for drinking water and thus the costs incurred drop.

Although Germany is a relatively water-rich country, yet our high quality of groundwater resources have come under pressure due to pollution and overexploitation. This requires support from deeper layers. Secondly, the municipal sewage systems are relieved, as well as the regional drinking water supply. Less water needs to be pumped and treated in the wastewater cycle because the water enters back into the natural cycle of evaporation and precipitation. This relieves the regional microclimate.

The rainwater also has the enormous advantage that almost no hardness appears. It can therefore be used without additional softening or reverse osmosis system for evaporative cooling systems, which in turn saves significant costs. For the above example, the amount of water required of 10.5 m³ in Germany can be collected on average over a roof area of approx. 13 m² as rainwater.

Certificates

The use of an adiabatic cooling of buildings with rainwater enables more and more often to obtain a certification. That way the quality criteria of the DGNB - "German Sustainable Building Council" require, among other things, environmental, economic and socio-cultural aspects for the certifications to be taken into account. These include less risks for the environment by preventing refrigerants, thermal comfort and indoor air quality, reduction of drinking water consumption and total energy demand, as well as the operating costs. The same applies to a LEED - "Leadership in Energy and Environmental Design" - certificate, which demands equally improved energy performances, good air quality, thermal comfort and monitoring of the CO2 emissions.

Sanitization

In order that the humidification with rainwater meets the relevant legal requirements, rules and guidelines for the protection of health and the environment, a treatment of rainwater must follow. It must be excluded that Legionella or other disease creators are formed in the exhaust air. For treatment, various methods can be performed. These include, for example, the membrane filtration to reverse osmosis or a chemical treatment with chlorine or ozone.

With the AQUALOOP membrane filtration of the INTEWA GmbH membranes with a pore size of 0.2 µm are used, which not only retain inorganic particles of adequate size but also germs. 99.9999% of bacteria and 99.7% of the viruses are removed. The membranes are designed for operation up to 10 years, hardly need maintenance, no continuous chemical cleaning and are therefore completely free of environmentally harmful disposable materials. That way, the rainwater can be used optimally for the operation of the adiabatic cooling.

The following system diagram shows the basic structure of a system for adiabatic cooling with rainwater and simultaneous rainwater harvesting for flushing toilets and garden irrigation. The rainwater is pre-filtered through the self-cleaning, highly efficient PURAIN filter. In order to guarantee the highest possible supply security, speedcontrolled RAINMASTER Favorit SC can be used with a redundant construction.

Via a floating suction filtration the particularly economical and quiet RAINMASTER Favorit-SC suck the cleanest water from the hybrid tank and supply the consumers, such as toilets, cleaning systems and gardens with valuable, clear and lime-low rainwater. A supplemental supply with drinking water takes place automatically with water shortage via the DVGW tested RAINMASTER.

  1. PURAIN rainwater filter

  2. Inlet calming

  3. Charge pump

  4. Pressure tube

  5. AQUALOOP membrane tank

  6. AQUALOOP membrane station

  7. Control AQUALOOP membrane station

  8. Float switch

  9. Clear water tank

10. RAINMASTER Favorit SC

 

Conclusion

In summary it can be stated that the adiabatic cooling is a particularly sustainable alternative to conventional types of cooling buildings with a savings potential of over 80%. By the evaporation of water, heat can be withdrawn from the air and so the air, which is supplied to the room can be cooled. In this way high energy costs can be saved and a positive impact on the climate protection is visible. Figure 4: example system adiabatic cooling with rainwater and rainwater harvesting, INTEWA GmbH It is ideal if rainwater can be used while doing so. Drinking water costs and resources will be saved and due to particularly lime-low rainwater, we could dispense with water softening systems. The treated rainwater with the AQUALOOP membrane filtration corresponds to all hygienic requirements of the local drinking water regulations. If there is sufficient rainwater available, even more consumers, such as toilets and garden irrigation can be connected to the system to additionally save water.

Dipl. Ing. Oliver Ringelstein

INTEWA GmbH

Auf der Hüls 182

D- 52068 Aachen

Phone: +49 (0) 241 96605 0