Figure 4. Representative Greenhouse Gas Emissions of District Energy and Building-Scale Heating Technologies.
n Building Systems
n District Heating
BLDG electric resisistance heating
DH natural gas boiler
BLDG natural gas boiler
BLDG air source heat pump heating only
DH natural gas turbine CHP
DH natural gas engine CHP
DH natural gas combined-cycle turbine CHP
BLDG ground source heat pump heating only
DH industrial waste heat recovery
DH biomass boiler
DH geothermal hot water
DH biogas boiler
DH biomass organic Rankine cycle CHP
DH municipal waste steam cycle CHP
DH biomass steam cycle CHP
DH biogas turbine CHP
DH biogas engine CHP
DH biogas combined-cycle turbine CHP
• Thermal grids have a demonstrated ability to decarbonize.
(0.20) (0.10) 0.00 0.10 0.20 0.30 0.40
Net GHG Emissions (metric tons CO2 equivalent per MWh delivered thermal energy)
Source: FVB Energy Inc., summarizing results from analysis for Fundamental Benefits of District Heating and Cooling to Society and a Model to Quantify and Evaluate the Benefits,
International Energy Agency Implementing Agreement on District Heating and Cooling including integration of CHP.
It can be argued that we should not compare district energy
with today’s power grid, because there is an ambition to
decarbonize the electricity grid through nuclear energy, wind
farms, tide, wave power, etc. By the same token, we should not
compare near-term district energy to a hoped-for future power
grid. We should compare the future power grid to the future
district energy system. It is intellectually inconsistent to assume
decarbonization of the power grid but not the thermal grid.
There are plenty of real-world examples of decarbonization of
thermal grids, as described in my First Quarter 2011 column.
• District energy strengthens and greens the power grid.
District energy provides multiple benefits to power grids
relative to efficiency, emissions and economics. First, district
cooling systems reduce peak power demand through the use
of chilled water or ice thermal energy storage, which shift
power demand from on-peak to off-peak periods. Second,
district energy CHP facilities generate power in high power
load areas and can be dispatched based on real-time peak
power pricing signals. For example, Princeton University cut
its peak power demand from 27 MW to 2 MW with a
combination of CHP, absorption chillers and thermal energy
storage. Hot water thermal storage can be used to maximize
CHP heat recovery by smoothing out the supply of heat
relative to demand. Third, district energy can facilitate increased
renewable power generation by helping balance the power
grid, as nondispatchable renewable generation sources (such
as wind and solar) increase.
Reductions in peak power demand or generation of CHP
power in high-load areas have multiple benefits. Electricity
transmission and distribution losses from remote power plants
are reduced, constraints in delivery of power to high-load areas
are relieved, reliability is increased and generation of power
using inefficient and polluting peaking plants is reduced.
District energy provides multiple benefits to power
grids relative to efficiency, emissions and economics.
• District energy complements other strategies. Relative to
building heating, it should not be an ’either/or’ choice – district
energy or (fill in the blank). Diversity of energy technologies and
energy sources helps reduce risks, and district energy can and
should be a part of the mix, particularly for higher-density areas,
where its economic and efficiency strengths are greatest, and
where its benefits to the power grid are maximized.
Mark Spurr is;legislative;director;of;IDEA.;He;also