What is Aquathermy, EOW, TEO, TEA and TED
Aquathermy is a collective term for extracting thermal energy from surface water (TEO), wastewater (TEA) or from the production of drinking water (TED). It is also called energy from surface water (EOW). The water has a temperature between 7 and 25 degrees; this is also called a very low temperature heat source (ZLT). One can also extract cold from surface water or drinking water, this also goes under the name Aquathermie. If one wants to use the hot water in the winter months, in many cases the heat will have to be upgraded to a higher temperature. This can be done by using a heat pump. Furthermore, the water can be stored temporarily, this is done in a heat and cold storage system (WKO).
Thermal energy from wastewater (TEA)
During the processing of wastewater at sewage pumping stations and WWTPs, the water can also have a temperature that can be used for heating. One can use either the influent (sewage, also called riothermal) or the effluent (treated sewage) for this purpose. Generally, the effluent is used with the added advantage that this water has already been purified and thus can cause less damage to the heat exchanger. On the other hand, a lot of energy is lost because, for example, the water from the shower, dishwasher and washing machine has already cooled down because it has been mixed with colder water. With a heat exchanger, influent water can be collected immediately to be used for heating. Thermal energy from wastewater is less seasonal (Wastewater is always available and provides constant low-temperature heat. Temperatures
Free-fall sewer heat exchanger internal
fluctuate between 12°C in winter and 20°C in summer) and so this often does not require a WKO plant. However, in order to guarantee the supply of heat at peak times (in winter), it is useful to store a buffer in the form of a WKO system in the summer. To extract heat from sewer pipes, one can use internal free-fall sewer heat exchangers (these can be placed in existing sewer pipes in scale sections) or external free-fall sewer heat exchangers.
Thermal energy from drinking water production (TED)
Due to climate changes, drinking water is subject to temperature fluctuations just like surface water. Therefore, thermal energy can be extracted from drinking water pipes. This can be done in three places; the raw water (untreated) that will be used for drinking water, the water in the ground or at the surface and the clean water (treated water). The energy from the clean water can be extracted where the water reserves are located or from the water that goes in the pipes to households and businesses. The main purpose here is to extract cold from the water for example to cool buildings. The average temperature of drinking water is 12°C. By pumping the drinking water through a heat exchanger, an exchange of heat or cold takes place. This can then be used directly in a building or it can be stored in a WKO (heat and cold storage system).
Benefits and sustainability TEO
It is estimated that TEO (thermal energy from surface water) can meet over 40% of the heat demand and 54% of the cold demand. An additional advantage of extracting warm water from surface water in the warm months is that the risk of blue-green algae and botulism is reduced. This is because the average water temperature goes down. Furthermore, the technology has little impact on urban planning. Solar farms and windmills take up much more space. People are striving more and more for natural gas-free neighborhoods This is a good alternative to natural gas because it has great potential to heat buildings in a sustainable way, especially in the Netherlands where water is abundant. By 2030, we want 80% of electricity to come from a renewable source. Extracting heat from a water source produces no CO2 emissions. Only the heat pump uses electricity; if this electricity is obtained from sustainable sources, the CO2 emissions are very limited and aquathermy is therefore very sustainable.
When is Aquathermy profitable and achievable
Building near the heat source and sufficient building density: laying pipes is expensive, so the distance from the source to buildings must be small. For a small project (for example, an office) this is a few hundred meters at most, for a large project (more than 10,000 homes) several kilometers at most. There must be a possibility to store the heat: the soil must be suitable for a WKO. How much heat the building needs and how well it is insulated is also important. If the heat required must be higher than 70 degrees then the energetic efficiency becomes too low, it is no longer profitable. In well-insulated buildings one can use low temperature heating. It will take some getting used to because with low-temperature heating it takes longer to heat a room.
There are current developments in which it is increasingly appealing to apply aquathermy. Heat pumps are getting better and better, and if storage of warmer water in the ground is allowed in the future, the efficiency will also improve.
Why is filtration important in aquathermy, TEO
The following components are required for a TEO system:
- An inlet point/work
- A (pre-)filter
- A pump
- A fine filter
- A heat exchanger
- Heat pump (if water needs further heating)
- Other auxiliary equipment (meters, fittings)
- An ATES installation (is not always required)
Filtration is an important component for several reasons:
Water streams generally contain many contaminants. This can affect the various components of the TEO system.
In a TEO system, heat and cold is extracted. This is done using a heat exchanger. To protect this equipment, it is important that the water first passes through a filter. In some systems, a heat pump is needed to raise temperatures a bit. Heat pumps are equipped with 60 mesh filter screens. It is important that the fluid passing through the pipes contain as little dirt as possible. If there is a lot of dirt in the piping system and it accumulates and clogs the screens, the series of heat pumps will fail. If the heat pumps fail, it will cost both time and money to get everything running again. So a thorough flushing and cleaning of the piping system is very important.
With a TEO system, you can find different types of contaminants in the water. There are fairly coarse contaminants such as driftwood, plastic, trash and fish. These will first have to be filtered with a coarse filter before the water is extracted from the surface by the pump. Also found amongst other things are microorganisms, plants, algae or other small animals or mussel seed. These are very harmful to the equipment and biological fouling (biofouling) can occur on the surfaces of the pipes or equipment. Biofouling or biological fouling is the accumulation of microorganisms, plants, algae or small animals where it is not wanted, like on surfaces such as ship and submarine hulls, equipment such as water intakes, pipes and grates. For example, a major culprit of biofouling is the guagga mussel. In areas where the guagga mussel is found in high densities, algae concentrations decrease and the water becomes clearer. So one might think that this is actually good for the intake water since the water becomes clearer, but the water quality does not necessarily improve. This is another reason why filtration remains important.
In addition, guagga mussels adhere to hard surfaces; they have great adhesive capacity. Furthermore, the guagga mussel is much more tolerant than other mussels to extreme conditions and is less sensitive to habitat disturbances. The guagga mussel can handle low temperatures very well. Because they attach so easily, they are very damaging to equipment and pipes. To prevent the mussel from attacking pipes and equipment, a good control technique is important. Many companies use chlorine bleach but other chemicals are also used. To prevent environmental pollution, it is not desirable to use a lot of chemicals, so one will have to extract most of the organisms with a good filter.
What to consider when choosing a filter for TEO
TEO (thermal energy from surface water) involves extracting water from a nearby stream, canal, river, pond or lake. First, the fine filter must be protected from coarse pollution and pump wear. A pre-filter is used for this purpose, several options are available for this. Depending on the situation a choice is made; what is the water depth, are there any water level fluctuations, is the place easily accessible and so on.
The first step is to install an intake filter for the pump. For this, an intake basket is usually placed in the water up to 250 m3/hr. If less maintenance is desired, a self-cleaning intake screen is chosen. The self-cleaning intake filters of Dutch Filtration have a filtration degree from 200 micron and larger. Pressure loss is minimal and there is a very low intake velocity with a very large open surface area. Underwater life is affected as little as possible.
Cleaning takes place through a booster pump that sprays 5-7 bar of water into the filter. If the screen is clogged, compressed air is injected at high speed to clean the screen.
The placement of the pre-filter is critical to the operation of the system. If it is placed too close to shore in shallow water, the filter will quickly clog up due to fouling. Also, it must not be a hazard and thus something must be placed around it, sometimes the intake well must even be placed behind the quay wall. Furthermore, the intake velocity must be approximately equal to that of the flow rate of the water.
Choosing a pump
For the pump, we also have several options:
Self-priming pump (25-50-100-250 m3/hr)
Circulation pump (25-50-100-250 m3/hr)
A self-priming pump can remove entrained air or other gases from the suction line. A standard circulation pump cannot do this. Compared to a circulation pump, the efficiency of a self-priming pump is somewhat lower and the pump must also be placed closer to the surface water.
The fine filter
Several self-cleaning options are available for a fine filter. In particular, the amount of space available and the amount of contamination in the surface water must be considered. Depending on the type of contamination present in the water, the mesh size of the filter must be selected (typically 20 – 500 microns).
Our range of fine filters includes:
Disc filters in TEO application
Automatic self-cleaning filter
To prevent fouling of guagga mussels, among others, we recommend filtering at 40 microns. A big advantage of the disc filters of Dutch Filtration is that it is a wide range with many options in micronage. One can filter as low as 10 microns, followed by 20, 40, 55, 70, 100, 130, 200 and 400 microns.
Another advantage of the disc filters is that the installation can consist of several identical batteries/skids linked together. This has many advantages with maintenance, engineering and possible expansion or phasability.
Several tests have been done with TEO installations and it appears that the most suitable solution consists of a self cleaning intake screen (available at Dutch Filtration as TIS Self cleaning intake screen) in combination with a Discfilter 40 micron (available at Dutch Filtration as Amiad Discfilter).
Of course one will always have to take several factors into account. Dutch Filtration can advise you in composing the filtration of your aquathermy system. We design and produce filters but can also supply your pump.
Glossary of terms:
EOW = Energy from surface water
TEO = Thermal Energy from Surface Water
TEA = Thermal Energy from Wastewater
TED = Thermal Energy from Drinking Water
CHP = Thermal Energy Storage
Riothermal = Thermal Energy from Wastewater from the sewer system
Aquathermie in de praktijk: eerste conclusies en inzichten: Netwerk Aquathermie in samenwerking met Deltares 30 januari 2020
Zeeuws energieakkoord: dossier aquathermie https://www.zeeuwsenergieakkoord.nl/bibliotheek/aquathermie
Expertise Centrum Warmte : Aquathermie https://www.expertisecentrumwarmte.nl/themas/technische+oplossingen/techniekfactsheets+energiebronnen/aquathermie+nieuw/default.aspx
Warming Up: Aquathermie configuraties https://www.warmingup.info/documenten/aquathermie-configuraties.pdf