Size Matters: the Importance of Choosing the Right CHP Unit

Posted by Ian Hopkins on 27-Sep-2016 10:00:00

Don't lose CHP efficiency by specifying the wrong sized Combined Heat and Power unit.

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Combined Heat and Power can save money and carbon, but when sized incorrectly it could just end up burning cash.

Based on a large hospital, below are three CHP sizing scenarios. the scenarios are based on the hospital’s base heat load, each plant would run from 7am - midnight, with 95% availability. It would include a heat rejection facility.

Our three scenarios are based on natural gas costs of 3.0p p/kWh, and electricity costs of 9.0p p/kWh, which is typical purchase price in the UK market today.

 

Under-sized

System specifications:

210 kWe electrical output

337 kW thermal output

669 kW fuel input

100% of the CHP unit’s energy is used by the building

Savings:

1238 MWh of electricity: £111,400

Displaced boiler fuel: £74,500

Total savings: £185,900

Operating cost:

Fuel: £110,400

Maintenance: £14,000

Total operating cost: £124,400

 

Overall:

Net savings: £61,500

Capital cost: £250,000

This system would pay for itself in 4.06 years

This system would save 342 tonnes of CO2 each year

Right-sized

System specifications:

530 kWe electrical output

648 kW thermal output

1484 kW fuel input

The building uses 90% of this unit’s heat throughout the year.

Savings:

3124 MWh of electricity: £281,200

Displaced boiler fuel: £128,900

Total savings: £410,100

Operating cost:

Fuel: £245,000

Maintenance: £45,000

Total operating cost: £290,000

Overall:

Net savings: £120,100

Capital cost: £400,000

The heat usage for this system goes down, as the cost of fuel goes up, but the big savings from increased electricity production mean that this CHP system pays for itself in 3.33 years.

This system would save 719 tonnes of CO2 each year

 

Over-sized

System specifications:

770 kWe electrical output

823 kW thermal output

2028 kW fuel input

The building uses 79% of this unit’s heat throughout the year.

Savings:

3631MWh of electricity: £326,800

Displaced boiler fuel: £114,600

Total savings: £441,400

Operating cost:

Fuel: £267,800

Maintenance: £55,000

Total operating cost: £322,800

Overall:

Net savings: £118,600

Capital cost: £600,000

This site is generating too much heat for the building to use, but still incurs large fuel and maintenance overheads. The system will still be profitable, but it will take longer: The client can expect it to pay for itself in 5.06 years

This system would save 731 tonnes of CO2 each year

Takeaways:

1. A CHP unit which is smaller than required will fall short on energy requirements.

2. A correctly sized CHP unit will deliver optimum cost and carbon dioxide savings.

3. A unit which is larger than required will fail to deliver the savings associated with CHP and miss out on beneficial CCL exemption.

Discover how to specify the right size of CHP unit in order to provide maximum return on investment. Get your free eGuide now: A guide to CHP unit sizing

                   

Topics: CHP / Cogeneration

Ian Hopkins

Ian Hopkins is a technical sales professional and business leader with more than 15 years’ experience in delivering energy efficiency projects and strategy in Europe and the United States. Ian currently heads up the Sales and Marketing function as one of the board directors at ENER-G Combined Power Ltd.