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What is the importance of a low return temperature
A heating system always has two pipes: through one pipe the hot water is pumped into the greenhouse and through the other the cooled water (return water) is pumped back to the boiler or other heat generator. If the return water is also used to cool flue gases or goes back into a geothermal heat source, the temperature must be as low as possible. With a low return temperature, the flue gases can be cooled down to well below the dew point, thus extracting more energy from the flue gases. In the case of geothermal heat or a heat cluster, as much energy as possible is used with a low return temperature; energy that would otherwise remain unused. In short: it is therefore important that the return temperature of this water is as low as possible. In this article we explain the importance and advantages of a low return temperature.
What is return temperature?
The return temperature is the temperature of the water in the pipe system after heat has been released into the greenhouse. The difference between inlet temperature and return temperature of the water occurs during transport through the heating system. A low return temperature is important for, among other things:
- Better use of the condensers of CHP and/or boiler
- Higher efficiency from each m³ of natural gas
- Preparation for connection to heat cluster or geothermal heat
- Larger useful capacity heat storage tank
Inlet temperature, flow and ambient temperature
The first three factors are linked. The inlet temperature, the flow and the ambient temperature in the greenhouse determine the heat output of the pipe and thus also the temperature of the water that flows back into the return pipe. If one of these factors changes, it affects the other factors.
For example, if the flow decreases while the supply and ambient temperatures remain the same, the water will circulate more slowly. As a result, heat emission and thus the return temperature decrease. If you want to keep the heat emission the same in this case, the supply temperature will have to rise.
With an increasing ambient temperature, the convection part of the heat emission decreases and the radiation part increases. At the convection temperatures used by growers in greenhouses, the ratio between convection and radiation is approximately 50% - 50%. A rising ambient temperature is detrimental to the convection of the pipe.
For example, if the flow decreases while the supply and ambient temperatures remain the same, the water will circulate more slowly. As a result, heat emission and thus the return temperature decrease. If you want to keep the heat emission the same in this case, the supply temperature will have to rise.
With an increasing ambient temperature, the convection part of the heat emission decreases and the radiation part increases. At the convection temperatures used by growers in greenhouses, the ratio between convection and radiation is approximately 50% - 50%. A rising ambient temperature is detrimental to the convection of the pipe.
Airflow
In order for a heating pipe to give off heat properly or to cool down, you need an unobstructed air flow around the pipe. In other words: it is essential that the ambient air can come into good contact with the pipe and that a natural circulation starts. Pipes should therefore hang "freely" (low-temperature hose network) or lie down (pipe rail system). The air flow then ensures that both heat as well as moisture and CO2 are evenly distributed throughout the greenhouse.
Return pollution
The last factor influencing the return temperature is the return pollution. Here you can think of non-optimal functioning installation parts, such as:
• Unregulated heating groups that circulate but have little or no output;
• A by-pass that is open;
• A coupling valve between the supply and return at the end of the transport pipe;
• Leak-through mixing valves (is actually closed);
• Return of a low temperature network mixed with the return of a high temperature network.
These factors cause hot supply water to enter the return, which pollutes (increases) the return temperature.
• Unregulated heating groups that circulate but have little or no output;
• A by-pass that is open;
• A coupling valve between the supply and return at the end of the transport pipe;
• Leak-through mixing valves (is actually closed);
• Return of a low temperature network mixed with the return of a high temperature network.
These factors cause hot supply water to enter the return, which pollutes (increases) the return temperature.
How do you realize a lower return temperature?
A lower return temperature can be achieved in many ways. Sometimes a circuit on a low-temperature heating network is sufficient to realise substantial savings. Other possible measures are adjusting the heating regime, cascading groups or adjusting the transport pipe.
A universal answer to the question of how to achieve a lower return temperature cannot be given, because this depends on the layout of the current heating system. Each operating situation is different and must be calculated separately. So always get good advice about this.
A universal answer to the question of how to achieve a lower return temperature cannot be given, because this depends on the layout of the current heating system. Each operating situation is different and must be calculated separately. So always get good advice about this.
What are the advantages of a lower return temperature?
An investment in lowering the return temperature pays for itself; lowering the return temperature from 50⁰C to 30⁰C can in theory even result in a capital gain of 5%. By sending water with a lower return temperature over the condenser of the CHP or the boiler, the flue gases condense better. As a result, more heat is recovered from the flue gases, which would otherwise disappear via the chimney. It also produces a higher efficiency of each m³ of natural gas. With a CHP, the return temperature is even more important than with a boiler, because with a CHP, flue gases only condense well at a lower temperature. This is due to the greater air excess during firing.
Furthermore, a lower return temperature can provide 10 to 20% more energy storage capacity in the storage tank.
Furthermore, a lower return temperature can provide 10 to 20% more energy storage capacity in the storage tank.
Contact form
Can't find your answer? Fill out the contact form and our specialist Ben Peters will get back to you. On weekdays, even within 24 hours.
Also interesting for you
What is the importance of a low return temperature
A heating system always has two pipes: through one pipe the hot water is pumped into the greenhouse and through the other the cooled water (return water) is pumped back to the boiler or other heat generator. If the return water is also used to cool flue gases or goes back into a geothermal heat source, the temperature must be as low as possible. With a low return temperature, the flue gases can be cooled down to well below the dew point, thus extracting more energy from the flue gases. In the case of geothermal heat or a heat cluster, as much energy as possible is used with a low return temperature; energy that would otherwise remain unused. In short: it is therefore important that the return temperature of this water is as low as possible. In this article we explain the importance and advantages of a low return temperature.
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Topics in this article
What is return temperature?
The return temperature is the temperature of the water in the pipe system after heat has been released into the greenhouse. The difference between inlet temperature and return temperature of the water occurs during transport through the heating system.
A low return temperature is important for, among other things:
- Better use of the condensers of CHP and/or boiler
- Higher efficiency from each m³ of natural gas
- Preparation for connection to heat cluster or geothermal heat
- Larger useful capacity heat storage tank
Inlet temperature, flow and ambient temperature
The first three factors are linked. The inlet temperature, the flow and the ambient temperature in the greenhouse determine the heat output of the pipe and thus also the temperature of the water that flows back into the return pipe. If one of these factors
changes, it affects the other factors.
For example, if the flow decreases while the supply and ambient temperatures remain the same, the water will circulate more slowly. As a result, heat emission and thus the return temperature decrease. If you want to keep the heat emission the same in this case, the supply temperature will have to rise.
With an increasing ambient temperature, the convection part of the heat emission decreases and the radiation part increases. At the convection temperatures used by growers in greenhouses, the ratio between convection and radiation is approximately 50% - 50%. A rising ambient temperature is detrimental to the convection of the pipe.
For example, if the flow decreases while the supply and ambient temperatures remain the same, the water will circulate more slowly. As a result, heat emission and thus the return temperature decrease. If you want to keep the heat emission the same in this case, the supply temperature will have to rise.
With an increasing ambient temperature, the convection part of the heat emission decreases and the radiation part increases. At the convection temperatures used by growers in greenhouses, the ratio between convection and radiation is approximately 50% - 50%. A rising ambient temperature is detrimental to the convection of the pipe.
Airflow
In order for a heating pipe to give off heat properly or to cool down, you need an unobstructed air flow around the pipe. In other words: it is essential that the ambient air can come into good contact with the pipe and that a natural circulation starts.
Pipes should therefore hang "freely" (low-temperature hose network) or lie down (pipe rail system). The air flow then ensures that both heat as well as moisture and CO2 are evenly distributed throughout the greenhouse.
Return pollution
The last factor influencing the return temperature is the return pollution. Here you can think of non-optimal functioning installation parts, such as:
• Unregulated heating groups that circulate but have little or no output;
• A by-pass that is open;
• A coupling valve between the supply and return at the end of the transport pipe;
• Leak-through mixing valves (is actually closed);
• Return of a low temperature network mixed with the return of a high temperature network.
These factors cause hot supply water to enter the return, which pollutes (increases) the return temperature.
• Unregulated heating groups that circulate but have little or no output;
• A by-pass that is open;
• A coupling valve between the supply and return at the end of the transport pipe;
• Leak-through mixing valves (is actually closed);
• Return of a low temperature network mixed with the return of a high temperature network.
These factors cause hot supply water to enter the return, which pollutes (increases) the return temperature.
How do you realize a lower return temperature?
A lower return temperature can be achieved in many ways. Sometimes a circuit on a low-temperature heating network is sufficient to realise substantial savings. Other possible measures are adjusting the heating regime, cascading groups or adjusting the
transport pipe.
A universal answer to the question of how to achieve a lower return temperature cannot be given, because this depends on the layout of the current heating system. Each operating situation is different and must be calculated separately. So always get good advice about this.
A universal answer to the question of how to achieve a lower return temperature cannot be given, because this depends on the layout of the current heating system. Each operating situation is different and must be calculated separately. So always get good advice about this.
What are the advantages of a lower return temperature?
An investment in lowering the return temperature pays for itself; lowering the return temperature from 50⁰C to 30⁰C can in theory even result in a capital gain of 5%. By sending water with a lower return temperature over the condenser of the CHP or the boiler, the flue gases condense better. As a result, more heat is recovered from the flue gases, which would otherwise disappear via the chimney. It also produces a higher efficiency of each m³ of natural gas. With a CHP, the return temperature is even more important than with a boiler, because with a CHP, flue gases only condense well at a lower temperature. This is due to the greater air excess during firing.
Furthermore, a lower return temperature can provide 10 to 20% more energy storage capacity in the storage tank.
Furthermore, a lower return temperature can provide 10 to 20% more energy storage capacity in the storage tank.
Contact form
Can't find your answer? Fill out the contact form and our specialist Ben Peters will get back to you. On weekdays, even within 24 hours.
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