In a combined heat and power unit, a gas-powered combustion engine drives a generator to produce electricity. The heat this creates is extracted from the coolant and exhaust gas via the heat exchanger and can then be utilised.
CHP unit – Heat and power for commercial use
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CHP unit for heat and power
The CHP units developed by Viessmann are designed for commercial and municipal use. Correspondingly, they have a high performance and are matched to the operational processes for a secure supply of electricity, heating/cooling as well as domestic hot water. This means that you are not only investing in greater efficiency, but also in the future.
Compact appliances from the Vitobloc 200 product range are designed as decentralised CHP units with a bias towards heating. These comparatively small units generate electricity for self-consumption. The heat that is generated by this process is used simultaneously, almost without losses, for heating. Any power not required is exported to the public grid and the power supply utility provides remuneration accordingly.
Why a combined heat and power unit (CHP)?
The majority of power generated in Germany is produced in condensation power stations. This means that heating energy is converted into electrical power via a steam turbine. The average efficiency of all conventional power stations is approximately 38 percent, which means that over 60 percent of the energy input is lost to the environment as unused waste heat.
A combined heat and power unit goes one step further here and uses the waste heat, which can increase the overall efficiency of the system. In the case of large-scale CHP systems, this is done via district heating pipelines. However, the potential is largely exhausted in the existing stock. Ultimately, it only works if there are also large heat consumers, such as a housing estate, near the power station.
This is where the idea of decentralised combined heat and power units (CHP) with a heating bias comes into its own. Power is generated in comparatively small units where the heat by-product does not have to be transported over long distances simultaneously (which would incur heat loss), but can be used directly on site. There are also no losses arising from power distribution.
Decentralised power supply with combined heat and power unit
Central power stations usually only produce electricity. The accumulating heat is lost. In contrast, combined heat and power (CHP) uses up to 36 percent less primary energy –– which means a significant reduction in energy costs.
Structure and function of a CHP unit
A CHP unit essentially consists of an engine, a synchronous generator and a heat exchanger. The synchronous generator, driven by the internal combustion engine (drive unit), generates a 3-phase alternating current with a frequency of 50 Hz and a voltage of 400 volts, which is generally used on site.
The low voltage grid (0.4 kV level) is used for the electrical connection. As a rule, CHP units are operated in parallel to the mains. In principle, however, they can also be used in mains substitution mode by deploying synchronous generators. Surplus power can be exported to the power supply utility's grid.
The engine generates heat that can be absorbed in the "internal cooling circuit" successively from the lubricating oil, the engine coolant and the exhaust gas, and transferred to the heating system via a plate heat exchanger.
This system of energy generation and utilisation is referred to as combined heat and power (CHP) generation because the mechanical energy (power) generated by the engine and the thermal energy (heat) given off by the engine as it drives the generator are both used simultaneously.
In order to make the use of a CHP unit economically viable, the appliance should run continuously for as long as possible. The longer a CHP unit can realistically transfer heat and power into a system, the sooner it will pay for itself. When it comes to sizing, apart from some exceptions (such as emergency power supply) the focus is on heat. The CHP unit is heat-led.
Permanent annual curve –– design of the output of a CHP unit
If we look at how the annual heating output typically is spread over a 12 month period (permanent annual line), it becomes clear that a CHP unit should not be oversized. Its thermal output is calculated in such a way that heat can still be transferred even at times of low load.
In order to achieve a runtime of at least 4500 hours, we can assume approximately 20 percent of the boiler output as thermal output of the CHP unit to provide heating for the building.
On the heating side, the CHP unit operates in parallel with a boiler. Both heat generators are connected to the heating system, the DHW heating or other heat consumers, such as a swimming pool.
Depending on the consumption profile of the building, it may make sense to use a heating water buffer cylinder so that the runtime of the CHP module can be as long and uninterrupted as possible.
On the power side, the first priority is to cover the building's self-consumption. If no more consumers are available, the electricity is fed into the public grid and remunerated.
Power: for self-consumption or for exporting to the grid
Electricity for use on site is generated in units tailored to the respective requirement. Any power not required is exported to the public grid and the power supply utility provides remuneration accordingly.
Heat: use efficiently and almost loss-free
However, the heat generated in a combined heat and power unit is not lost, unlike with central power stations. The heat is fed into the heating network. Together with another heat generator, such as a boiler, the building is supplied with power, heat and DHW almost loss-free. Also, the cooling demand can be completely or partially covered by coupling with an absorption cooling machine.
The picture shows the schematic of a system integration for a CHP unit
Display of a Vitobloc 300 type NG
Since a CHP unit essentially pays for itself by reducing the amount of power drawn from the grid (and not through the feed-in remuneration), the consumption of electrical energy in the building must also be taken into account. By answering three simple questions, you can quickly check whether it makes sense to use a Vitobloc CHP unit:
- Is the required boiler output above 60 kW or the gas consumption in excess of 90000 kWh/a (relative to the gross calorific value)?
- Is the annual power consumption in excess of 32000 kWh?
- Are heat and power consumed simultaneously?
If the answer to all of these questions is "yes" and a gas connection is available, it is worth looking more closely into using a CHP unit.
Vitobloc 200 and 300 – compact, quiet and supplied ready-to-connect
Vitobloc 300 NG 15 and Vitobloc 300 NG 20 are compact, ready-to-connect units with water-cooled synchronous generators for producing three-phase power and heating water. With their low operating noise and small space requirement, they are suitable for new build and modernisation projects alike.
The Vitobloc 300 CHP units are suitable for natural gas, bio natural gas, LPG and the admixture of 20 percent hydrogen. The integrated condensing technology enables you to achieve an overall efficiency of up to 107.3 percent (Vitobloc 300 type NG 20).
The Vitobloc 200 series
CHP units such as the Vitobloc 200 type EM-260/390 or the Vitobloc 200 type EM-100/167 from Viessmann achieve impressive efficiency. The Vitobloc 200 CHP units are therefore particularly easy to maintain with their maintenance intervals. Some have integrated condensing technology and thus achieve an overall efficiency of up to 95 percent. And they are up to 50 percent electrically modulated and can be run with both heat-led and power-led operation. Other plus points for the Vitobloc 200 CHP unit are the extensive technical equipment with electricity meter and flexible connections for gas, flue gas, extract air and heating water, as well as the standard silencer hood for significantly reduced operating noise.
CHP units – efficient gas-operated systems for combined heat and power generation
Gas-operated combined heat and power units (CHP) generate electrical energy and heat simultaneously according to the principle of combined heat and power. A special gas combustion engine designed for heavy duty cycles drives the generator to produce electricity. These units are sized to suit residential complexes and commercial operations. On the heating side, the CHP unit operates in parallel with a boiler. Both heat generators are connected to the heating system in order to provide heating water or DHW.
Viessmann CHP units are team players. They achieve their highest efficiency in a system that is individually matched to the respective requirements. This starts with system technology, for example, with control cabinets for higher level control functions, and extends to customised maintenance contracts.
Product range: CHP units up to 530 kWel and 660 kWth
A CHP unit is extremely environmentally responsible: in addition to primary energy savings of up to 36 percent, CO₂ emissions are significantly lower compared to the conventional generation of power and heat. With more than 25 years' experience in this product area, Viessmann offers efficient gas operated systems for combined heat and power generation. Alongside standard products, the company also manufactures CHP units tailored specifically to customers' individual needs.