The goal of the R&D department was to develop a simple, robust, economical and durable system which can be used both in existing and in new channels. Critical success parameters, which affected the development considerably, were an outstanding economy and environment-friendliness.

Questions of the maintenance people:

• a possible set-up of the biological cleaning stage in the waste water treatment unit, designed for a temperature of 10-13°C / 50-55 F
• The lack of a suitable heat exchanger with very high heat transmission coefficient, which could avoid - when built-in - blockages in the channel.

These challenges to the development were solved technically and economically. The system RABTHERM was constantly developed since 1998 and used successfully in many facilities world-wide.

Important milestones of the development phase were:

• Investigation of the influence of waste heat utilization on the clarifying process in waste water cleaning plants in co-operation with EAWAG, Switzerland.
• Installation of treated and untreated steel plates into sewers for the clarification of the corrosion and erosion behavior. Annual control and measurement of the metal întensity as well as the long-term behaviour were accomplished in co-operation with EMPA, Switzerland, and the Swiss Institut for corrosion protection. As a final result of this development phase RABTHERM heat exchangers were certified with a minimum life span of 50 years.
• Execution of numerous feasibility studies and development of an own computation method for the regulation of hydraulic and thermal system parameters for the practical system implementation.
• Proof of economy, environmental compatibility by numerous studies and scientific research work.
• Measurements of different prototypes and pilot facilities for the improvement of the hydraulic characteristics of the system
• Improvement of the connection technique of the heat exchangers and their installation into sewers
• Optimization of the heat exchanger structure with an Anti-fouling system on the surface of the heat exchanger. The patented solution successfully prevents the degradation of the heat transfer during the operating phase.

Buildings with high heating and/or cooling demand. Compared with conventional energy sources, RABTHERM systems provide many advantages.

Market: Buildings with high heating and/or cooling demand, such as:

• Public and administration buildings, schools, sports facilities, swimming pools
• Commercial and industrial facilities, shopping malls
• Condominiums

Customer Benefit: Compared with conventional energy sources, RABTHERM systems provide advantages such as:

• Independence from foreign, fossil energy sources
• Primary energy cost reduction: 20-30 %
• CO₂ reduction: 30-85 %
• Fine dust: none
• Return on investment: 2 to 6 years
• Höhere Wärmepumpeneffizienz dank hohem Abwassertemperaturniveau

References:
Here wie have colleced son Reference projects for you. A complete list of all projects is available on demand. We are glad to present our reference projects in a personal presentation.

So far the warm water from showers, washing machines and buckets flows unused through drains up to the next sewage purification plant. The Rabtherm principle is simple and efficient: The lukewarm waste water is cooled down around maximum 2,0 °C (3,5 F) (maximum 0,5 °C / 1 F over a 24-hour-day). The energy is transported by long-distance pipe to the respective buildings. By heat pumps the temperature is brought up to 65 °C (150 F) for heating and warm-water supply.

In the heat exchanger, heat is extracted from the waste water and supplied through an intermediary thermal unit heat carrier (ITUHC) to the heat pump. The ITHUHC (pure water) between heat pump (heat production) and heat exchanger (extraction of heat) runs through a plastic tube. A distribution pipe feeds each of the 1 to 3 m long heat exchangers. Afterwards the ITUHC is collected in the return collecting pipe and flows back to the heat pumps.

The heat exchanger is built in a concrete cast iron or plastic sewer and has a service life of at least 50 years. Corrosion, erosion/abrasion, tightness, fouling, channel maintenance and cleaning are some factors, that influence the strict quality assurance criteria on material choice, construction, production (welding) and assembly/installation. Parallel to the quality assurance also all possible remedy scenarios were set according to „the principle“ determination-identification-repair.

The heat exchangers can be installed both in drains of new buildings and when reorganizing existing systems. A cubic meter waste water, corresponds to about five bath tubs, in this case the heat exchanger wins two to three kilowatt-hours energy. An energy-saving lamp burns 200 to 300 hours. In this way a RABTHERM facility can reduce fuel consumption by 60-70 %. Even with a tubing downward gradient of under one per cent or in overflow channels the system can be used.

How much costs the energy system of RABTHERM?

Facilities (extraction of heat + heat production)

• € 2000 per attached appartment / USD 2900
• € 2000 per KW of attached power output / USD 2900

Heat exchanger

• The heat exchanger as an element without installation costs approx. 8-15% of the total system value.

Operating cost

• The saving of operating cost changes due to different heating systems and can amount up to 50 % of the annual costs.
• The RABTHERM system is nationally supported in most countries. Returning time on investments can be lowered by 30%.