District Energy & Combined Heat and Power
District Energy
In 2001, at their annual meeting, the International District Energy Association (IDEA) presented Cornell University's Utilities Department their 2001 System of the Year award. By an unanimous vote, the Cornell campus chilled water (including Lake Source Cooling), central steam, and co-generation (central heat and power) systems were recognized as the outstanding systems in the district energy industry in 2001.
Also, on September 23, 2013, at the 3rd Annual Global District Energy Climate Awards ceremony in New Your City, Cornell University's Utilities group was awarded the 2013 "Award of Excellence - Campus System". Cornell was internationally recognized for its outstanding achievement in demonstrating local district energy leadership in providing clean, sustainable energy solutions to protect against the risk of climate change with the use of Lake Source Cooling and the Combined Heat and Power Plant.
District energy systems produce hot water, steam or chilled water at a central plant and then distribute the energy through underground pipes to buildings connected to the system. Individual buildings do not need boilers, chillers or cooling towers. Customers use the hot and chilled water to meet their space heating, water heating, processing and air-conditioning needs. Once used in customer buildings, the water is returned to the central plant to be reheated and re-chilled and then recirculated through the closed-loop piping system. The benefits of this system include:
- Improved energy efficiency
- Enhanced environmental protection
- Fuel flexibility
- Ease of operation and maintenance
- Reliability
- Comfort and convenience for customers
- Decreased life-cycle costs
- Decreased building capital costs
- Improved architectural design flexibility
Combined Heat and Power
Also known as co-generation, combined heat and power is a way to increase the efficiency of power plants. Standard power plants effectively use just 40 percent of the fuel they burn to produce electricity. Sixty percent of the fuel used in the electric production process ends up being rejected or "wasted" up the smokestack.
This reject heat from a combined heat and power plant can be used to heat buildings in a surrounding area through a district energy system. Combined heat and power is only possible when there is an area near the plant that has a need for the heat – a downtown area, a college campus or an industrial development.
If one of our nation's energy challenges is lack of power, what if we doubled the efficiency of as many power plants as possible and got more energy for every gallon of oil or ton of coal they burn? Combined heat and power can help us do just that – and even help the environment in the process since less heat and fewer emissions will be rejected into the atmosphere.
Please visit the website of the International District Energy Association to learn more.
Energy Conservation Efforts (Supply Side)
District Heating System
Distributed digital process control
Boiler and plant controls were converted in 1985 to new digital (microprocessor) equipment that provides much higher reliability, accuracy and automation. Boiler dispatch is optimized providing the lowest fuel use for the plant as it provides steam to the campus for heating. The level of information and automation available allows the 24 hour operations staff of the plant to make much better decisions regarding operating costs and efficiency.
Boiler oxygen sensors
Oxygen sensors were added in boilers in 1990 to minimize excess air passing through the boilers beyond that necessary to completely combust the fuel supply. Any deviation from the required values for the boilers can be tracked, and causes identified, maximizing boiler combustion efficiency and minimizing fuel use.
Economizer feed water pre-heaters
All of the primary boilers for steam generation utilize an extra feature that recovers heat from the combustion gases leaving the boiler to preheat the feed water coming in. This extra feature scavenges extra heat from the waste gases, leaving the boilers improving overall efficiency and minimizing fuel use. In addition, our largest boiler utilizes an air pre-heater to preheat combustion air using waste energy that would otherwise be lost to the environment.
Co-generation of electric energy
In 1985 the heating plant pressure was doubled to 400 psig and back-pressure steam turbine electric generators were added which now generate 30 million kWh per year of electricity (nearly 12% of total campus use) at about twice the thermal efficiency of conventional power plants. Nearly all steam generated to heat the campus is passed through the turbines to generate electricity before it flows to the buildings and is condensed as a heat source. A conventional power plant throws away this "heat of condensation" which is why our "co-generated" electricity (generated together with steam which is used for heat) requires only half the normal energy input. A typical power plant efficiency is 35-45%, while the Cornell c-generated electricity is made at about 70% efficiency.
Turbine heat recovery
As part of the design for the turbines, all waste heat from the generators and bearings normally lost to the atmosphere was combined in a centralized heat recovery system with dedicated heat exchangers and piping. This heat is used to preheat boiler feedwater in the plant minimizing fuel use.
Optimized turbine dispatch
The control logic for the turbines was modified in 1995 to allow steam flow through the turbines to control pressure of the distribution system. This complicated control logic change minimizes, to the greatest extent possible, any steam bypassing the turbines, and maximizes the amount of electricity co-generated.
Auxiliary equipment variable speed drives
Nearly 150 horsepower of pumps and 800 horsepower of fans in the plant utilize variable speed drives to minimize energy input and optimize equipment control. The end result is better control of plant operations, reduced maintenance, and minimized electric energy input for auxiliary equipment operation.
Lower plant export pressure initiative
Over a 15 year period from 1985 to 2000 an aggressive program was instituted to lower the steam pressure required in the distribution system and the buildings. This has resulted in significantly lower pressures leaving the heating plant at all hours during the year. This increases the ability of the co-generation turbines to make electricity and the cooler steam temperatures have reduced heat losses from the piping system to the environment. The lower pressures and temperatures have also minimized wear and tear on all equipment and piping.
Boiler 6 and 7 replacement
These are the two primary boilers in the Central Heating Plant. They utilize high efficiency dual fuel (oil and gas) units with state of the art controls and economizers to reduce fuel use and add new firm capacity.
Steam distribution system leak repair and insulation upgrades
Over the past 15 years, a significant renewal program has replaced large segments of the steam distribution piping, some of which dated back to the 1920's. This program has reduced steam leaks and heat losses through piping insulation on a very large scale. This successful program will continue for at least another five years at which time nearly all of the main system segments will be renewed.