Hybrid Energy Systems in Future Low Carbon Buildings
 
Scope  
Background  
Micro wind  
Heat pumps  
Heat recovery  
Solar thermal panels  
Pv  
Bipvt  
Chp  
EarthToAir heat exchange  
Passive design  
Thermal storage  
Design concept  
Hybrid concept  
Methodology  
Modelling tools  
Case study results  
Environmental impact  
  


CHP - Background Information
What is CHP:

CHP (combined heat and power) are systems that produce electrical and thermal loads at the same time. Until recently the production of the electricity was made in power plants where huge amounts of heat energy were lost in the environment. The principal idea of CHP is to take advantage of the thermal energy from the production of electricity. Thus, CHP are high efficiency systems.
Micro CHP unit

As micro CHP the EU (2004/8/EC) 1 has defined small scale systems (less than 50 kW). These usually are applied for space and water heating to individual dwellings and small commercial buildings replacing the conventional boilers.

CHP provide furthermore fuel savings, reducing as a result emitted gases and the operational cost. The systems can function in parallel to the grid exporting energy or backing it up in case of a break down.

Micro CHP seems like a promising new solution with substantial growth and prospects being appreciated worldwide. Governments consider these systems as reliable solutions. Industry is developing new technologies, introducing alternative fuels and making the systems simpler and more accessible to all.

Types of engines and fuels:

Micro CHP are simple systems easily installed. They require roughly the same space with a boiler and are sound insulated. The most commercial systems are the ICE (internal combustion engines) while the external combustion engines such as Stirling engines, micro gas turbines and ORC (Organic rankin cycle) systems are aiming for the biggest market share. Fuel cells are still not commercially available.

Micro CHP are usually gas or petroleum fueled. However alternatives like biomass have become available maintaining high efficiencies and reducing carbon emissions to minimum levels.

How micro CHP operate:

Micro CHP systems are installed more or less as conventional boilers. They have similar volume and noise regulations.

External combustion engines:

Most of the micro CHP systems are external combustion engines such as Stirling and rankin

cycle engines. These systems are providing higher efficiency, can work with various types of fuel, have low gas emissions, low levels of noise and vibration. External combustion engines are using a part of fuel gas to drive the engine and produce electricity. The fuel (helium, hydrogen, etc) is been preheated in a heater alternator. Due to the external combustion, damages to the engine are limited, but require good isolation to avoid leakage. Main disadvantage is the reliable life span. External combustion engine


Internal combustion engine Internal combustion engines:

These are more popular in bigger scale systems. Currently industry is constructing high efficiency engines also in small scale systems. These engines are applicable to a wide range of usage and their operation can work also with liquid and gas fuels. Their operation is similar to car engines. Their main disadvantage is high maintenance cost and higher level of noise and gas emissions.



Fuel cells:

Fuel cells are electrochemical engines that convert chemical energy of fuel to electricity without combustion. The principal operation is that hydrogen and oxygen reacting with an electrolyte produce water electricity

and heat. Main advantages of fuel cells are high electricity efficiency, easy in usage, low level of noise and emissions. Due to the high efficiency and the type of fuel are used the emissions are 10 to 100 times lower than other system. The disadvantages that are limiting their popularity are high cost and low lifetime. Two most common types of fuel cell systems are the PEM (Proton Exchange Membrane) and SOFC (Solid Oxide Fuel Cells). Fuel cells


Commercial status:

External combustion engines are more popular in Europe, while in America internal combustion engines prevail. The Japanese market is focused mostly on fuel cells. Generally, fuel cells seem to be a more promising technology due to the advantages over internal and external combustion engines such as the high efficiency in electricity production, low gas emissions, independent of high heat demand and more suitable for future buildings. However, the cost is very high and their lifetime very short.

The tables below are showing the efficiencies for different micro CHP systems and their prices.


 External combustion Electrical (kWe) Thermal (kWt) Cost (£)
 WhisperGen 1 8 6 - 8000
 Microgen 1 3 - 24 6 - 8000
 Genlec 1 10 -
 OTAG 0.2 - 3 2 - 16 -
Table 1: reference No 2

 ICE Electrical (kWe) Thermal (kWt) Cost (£)
 Ecowill 1 3 5600
 Baxi Dachs 5.3 10.4 13000
 Ecopower 4.5 12 -
 EC Power 4-13 17-29 23000
Table 2: reference No 2

 Fuel Cells Electrical (kWe) Thermal (kWt) Cost (£)
 Hexis 1 2.5 -
 Ceramic 1 0.3 -
 Vaillant 1-4.6 25-50 -
 Baxi Innotech 1 2-40 -
Table 3: reference No 2

Micro CHP systems can convert more than 80% of the fuel energy to electricity and heat.

UK government support micro CHP installation recognizing the contribution of these systems concerning CO2 emissions. That is why from 1st April of 2010 no permission for installation of micro CHP systems shall be further required.

The table below represents the economical benefits of a micro CHP.


 Annual heating demand 18000 kWh
 Running Hours 3000 hours
 Electricity Generated 2400 kWh
 Unit cost avoid import 6.5 p/kWh
 Value avoiding import 133 £
 Export value 2.5 p/kWh
 Own use of Generation 85 %
 Value of export 9 £
 Marginal cost of unit 500 £
 Simple payback 3-4 Years
Table 4: reference No 3


References

1. Access to European Union law(eur-lex.europa.eu)
2. Combined heat and power, last update 1 November 2009 - ender day 1 - 15 April 2010
3. Harrison J., Micro Combined Heat & Power (CHP) for housing, 3rd International Conference on Sustainable Energy Technologies. Nottingham, UK, 28-30 June 2004
4. Government cash reward for microCHP, Combined Heat and Power Association, press release 5 February 2010

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