With a NYMEX natural gas futures contract now below $2.50 (January 2012), down from $14+ in 2005 and 2008, and with decades of supply available domestically, the evaluation of systems using natural gas for heating versus ground source heat pumps is compelling, particularly when combined with a Dual Fan Double Duct air system.

Systems Comparison

#	Description	Ground Source HP	DFDD
1	Land for Ground Loop	YES	NO
2	Vertical Bores	YES	NO
3	Loop Piping	YES	NO
4	Loop Pumps	YES	NO
5	Loop Pump Electrical	YES	NO
6	Water and Glycol	YES	NO
7	In Building Piping	YES	NO
8	Air Handling Fans	YES	YES
9	Variable Frequency Drives	YES (if used)	YES
10	DX Piping	NO	YES
11	Gas Meter and Piping	NO	YES
12	Additional Ductwork	NO	YES
13	Second Supply Fan	NO	YES
14	Terminal Box	NO (unless VAV)	YES

Operating Costs

#	Description	Ground Source HP	DFDD
1	Purchase Natural Gas	NO	YES
2	Pumping KW	YES	NO
Most of the time the DFDD fan VFDs run at reduced speed resulting in fan energy savings.

Maintenance

#	Description	Ground Source HP	DFDD
1	Water systems	YES	NO
2	Gas HX and Controls	NO	YES
The use of a DFDD system easily accommodates COSATRON grids which result in approximately a 30% reduction in required ventilation air. COSATRON systems can be applied to water source heat pump systems if low pressure drop MERV 13 CIMATEC filters are used. Visit - http://www.ga.wa.gov/eas/elcca/reports/DFDDSchool.pdf for an article on DFDD systems.

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