Combined heat and power — or CHP — has been around since Thomas Edison, who engineered a CHP system into the world’s first commercial power plant. Frequently referred to as cogeneration, CHP produces both heat and electric power from a single fuel source, while capturing the vast majority of energy typically lost in power generation. Trigeneration is also commonly referenced in this discussion — referring to onsite power, heating, and cooling generation.
If we had the technical capability to be “green” more than a century ago, how did we wind up where we are today, with most of our generated energy turning into thermal loss? Typically, in the traditional heat and power system, where power from the grid and onsite boilers provides heat, the overall plant efficiency is less than 50 percent. Comparatively, a CHP system is approximately 80 to 85 percent efficient.
While Edison was on to something and decentralized CHP systems in municipalities and industrial sites became the backbone of the emerging U.S. power industry, market forces were in play. The industry, looking to “bigger and better,” began building large, centralized power generation facilities. Wasted energy was an afterthought, if thought about at all for many decades.
According to the U.S. Department of Energy, more energy is lost as wasted heat in U.S. power generation annually than is used by the country of Japan. But what goes around, comes around. Today’s market and global economic forces, geo-politics, environmental concerns and focus on operating costs are all leading industry back to more efficient, flexible, and reliable on-site combined heat and power generation. With a nudge from the “powers that be”: President Obama declared that generating 40 gigawatts of new, cost-effective CHP by 2020 would be the national goal. The Department of Energy estimates that doing so would save manufacturers $10 billion annually in energy costs, drive $40 to $80 billion in new commercial capex investments, create jobs and reduce carbon pollution by 150 metric tons — equal to the emissions of 25 million cars.
CHP 101
Let’s say your facility currently purchases electricity from your local utility, while burning fuel in your on-site furnace or boiler for heating — a standard separate heat and power (SHP) system. According to the Oak Ridge National Laboratory, the average efficiency deploying this system is 45 percent. Pressures on your operating budget, combined with the uncertainties of external utility, regulatory, reliability, and environmental concerns, nudge you towards changing your ways.
Welcome to the brave new (old – remember Edison) world of CHP. Below is a condensed, “CliffsNotes” explanation of how CHP works, courtesy of the EPA’s Combined Heat and Power Partnership:
- “Every CHP application involves the recovery of otherwise wasted thermal energy to produce useful thermal energy or electricity. CHP can be configured as either a topping or bottoming cycle.”
- “In a typical topping cycle system, fuel is combusted in a prime mover such as a gas turbine or reciprocating engine to generate electricity. Energy normally lost in the prime mover’s hot exhaust and cooling systems is instead recovered to provide heat for industrial processes, hot water, or for space heating, cooling, and dehumidification.”
- “In a bottoming cycle system, also referred to as ‘waste heat recovery,’ fuel is combusted to provide thermal input to a furnace or other industrial process and heat rejected from the process is then used for electricity production.”
The hard sell: Benefits
Facilities with controlled environments, whether cleanrooms, dry rooms, or highly integrated specialty labs, are hallmarked by their high levels of energy and water consumption year round, driven in large part by strict parameters controlling process, air purity, humidification, and temperature control. Many controlled environment facilities, especially in the manufacturing sector, operate 24/7, with minimally scheduled down time for maintenance. Inadvertent lines down events are costly. The benefits of CHP are both specific to the facility deploying the technology, while also driving policy considerations on the national stage:
- Reduced overall energy costs
- Increased reliability
- Avoidance of costly power outages and production downtime
- Long lifecycle capital equipment
- Reliable predictability of future operating costs, while removing or minimizing the impact of external geopolitics, public policy decisions and economic forces on operating budgets
- Consumption of almost zero water resources in electricity generation. A typical coal fired power plant uses 0.2 to 0.6 gallons of water for each kWh produced. (EPRI, Water and Sustainability: U.S. Water Consumption for Power Production – The Next Half Century)
- Cost-effective way to add new electric generating capacity
- Reduced production of pollutants. The EPA estimates “CHP can reduce GHGs (greenhouse gases) and other air pollutants by 40 percent or more”
- Reduced grid congestion
- Improved electric distribution system reliability
Benefit/cost comparison to other clean technologies
The choice between technologies offering reliability, improved efficiencies, potentially lower life cycle costs, and reasonable maintenance can be dizzying and the subject of a lengthy article. The EPA summarizes the benefits and costs of CHP as compared to other clean energy technologies, below. It is important to align the CHP thermal load with the facility thermal load to maximize the plant efficiencies and minimize emissions.
Category |
10 MW CHP |
10 MW Wind |
10 MW Natural Gas Combined Cycle |
Annual Capacity Factor |
85% |
34% |
70% |
Annual Electricity |
74,446 MWh |
29,784 MHw |
61,320 MHw |
Annual Useful Heat |
103,417 MWht |
None |
None |
Footprint Required |
6,000 sq. ft. |
76,000 sq. ft. |
N/A |
Capital Cost |
$20 million |
$24.4 million |
$9.8 million |
Cost of Power* |
7.6¢/kWh |
7.5¢/kWh |
6.1¢/kWh |
Annual Energy Savings |
316,218 MMBtu |
306,871 MMBtu |
163,724 MMBtu |
Annual CO2 Savings |
42,506 tons |
27,546 tons |
28,233 tons |
Annual NOx Savings |
87.8 tons |
36.4 tons |
61.9 tons |
Table Assumptions: 10 MW Gas Turbine CHP — 28% electric efficiency, 68% total efficiency, 15 PPM NOx; Electricity displaces National All Fossil Average Generation (eGRID 2010) — 9,720 Btu/kWh, 1,745 lbs CO2/MWh, 2.3078 lbs NOx/MWh, 6% T&D loss; Thermal displaces 80% efficient on-site natural gas boiler with 0.1 lb/MMBtu NOx emissions; NGCC NOx emissions = 9 ppm; DOE EIA Annual Energy Outlook 2011 assumptions for Capacity Factor, Capital cost, and O&M cost of 7 MW utility scale Wind (1.5 to 3 MW modules) and 540 MW NGCC; Capital charges based on: 7% interest, 30 year life for PV, Wind and NGCC, 9% interest, 20 year life for CHP; CHP and NGCC fuel price = $6.00/MMBtu. Source: CHP & EPA Combined Heat and Power Partnership |
Selected technologies overview
How to best deploy CHP, and which technologies to utilize, require careful engineering and operations review. Following is a brief, high level discussion of CHP technologies, their features and benefits:
- Steam turbine:
- Large range of outputs: 100 kW to 250 MW.
- Turbines can be built on-site for efficiency and last for decades.
- Custom turbines maximize efficiency and thermal output.
- Fuel flexibility: able to utilize coal, oil, gas, wood biomass, or landfill gases.
- High pressure requires special operators: may need to add staff which could negate economic benefits.
- Combustion turbine:
- Size range: 500 kW to 300 MW.
- High quality heat — steam or hot water.
- Lifespan: 50,000 to 100,000 hours.
- Fuel options: single or multiple:
- Natural gas (must be high pressure)
- Landfill gas (high pressure)
- Fuel oil.
- On-site gas compressors need to be considered for initial, operating and ongoing maintenance costs.
- Low emission:
- Natural gas below 25 PPM NOx
- Low CO: 10 to 50 PPM.
- Selective catalytic reduction (SCR) further reduces emissions.
- SCR after treatment for the lowest emissions. Note: SCR approaches all add costs and require additional considerations in their deployment.
- Part load challenges — messing with your power output creates operational problems.
- Reciprocating engine:
- Size range: 10 kW to 18 Mw: smaller size makes it appropriate for many applications.
- Basic technology: more adaptable; easier for maintenance staff; better understood.
- Consider it an automobile engine on steroids.
- Hot water/Low pressure steam.
- Fast start/black start capable.
- Part load performance capable.
- Natural gas or diesel fueled — natural gas has had a cost advantage in recent years.
- Micro-Turbine
- Size range: 30 to 330 kW.
- No water required.
- Output range/Modular packages
- Provides Stepped capacity and redundancy.
- Fuel options:
- Natural
- Landfill
- Fuel oil.
- 40,000 to 80,000 hour lifespan of the engine.
- Applicability to phased projects: can add modules as the load increases.
- Emissions: low NOx.
- Add CO/VOC Catalyst to meet CA regulations.
- Compact, easier to fit into existing facilities.
- Fuel cells
- Start at 0.7 kW.
- Intriguing but expensive.
- High quality power.
- Very low emissions.
- Very quiet and few moving parts.
- Two most viable options for private sector: Phosphoric acid (PAFC) and Molten Carbonite (MCFC) produce high temperature output. The other available fuel cell technologies are most widely applied in the military.
Final considerations
A myriad of factors beyond the engineering and operational data points must be analyzed when considering a CHP installation. A simplified recipe for CHP success includes:
- Striking a balance between meeting electrical and facility heating/cooling loads;
- Having an affordable and reliable fuel source;
- Performance: Important to analyze the value of the energy you get out of the system vs. the energy input. A ratio of 4 or 5 to 1 or higher is ideal. This is referred to as spark spread performance;
- Maintenance: Include a percentage of cost for each kW hour generated in a set-aside account, banked to pay for routine maintenance and engine rebuilds down the road; and
- Incentives/Rebates – Programs vary geographically but are key factors driving affordability and adoption.
Mike Chonko, PE, CEM, directs mechanical engineering at SMRT Architects and Engineers. A Certified Energy Manager and licensed mechanical engineer, Mike has more than 20 years’ experience solving complex challenges for clients in science/technology/industry, healthcare, government, justice, and education. His passion: developing energy systems that are operationally and financially sound, yet highly efficient. [email protected]; www.smrtinc.com
This article appeared in the November/December 2015 issue of Controlled Environments.