Consulting-Specifying Engineer - August 2007 - (Page 44)

How To B E AT T H E C O D E S to the cost-per-ton of ice storage. Storage Chiller 1,600 1,400 1,200 1,000 Stored Cooling How much room do you need? Typical designs call for the ice storage to supply about 30% of the cooling required on a design day. Full storage space required 70 sq. ft. / tank 500 sq.ft./ ton x 20 ton/ tank = 0.70% of conditioned space Tons 800 600 400 200 0 12 am 2 4 6 8 10 12pm 2 4 6 8 10 12 am = Time of day Figure 2: Ice-system-operation design day Partial storage (30% of peak) = 0.70% x 33% = 0.23% The equations demonstrate that on average the space required for a partial ice storage system is relative to the water heater space required in a typical home. They also show that 0.23% of the conditioned space is required for an ice storage footprint. In the partial ice storage example space was required for the ice tank farm but space was not needed for the third chiller and associated cooling tower required by the conventional system. Because cooling systems seldom operate at full load, utilities struggle to plan and provide for increasing demand. This forces designers to create more sustainable buildings, and also forces the HVAC design paradigm to change regarding capacity safety factor and redundancy. Instead of adding 20% chiller capacity to a design day building peak load, reduce chiller capacity by at least 20% and add ice storage for safety factor. The ice storage is practically free and provides lower operating costs with increased efficiency, lower environmental impact and operational flexibility. References 1. Source Energy and Environmental Impacts of Thermal Energy Storage, Report #500-95-005, California Energy Commission, 1996, www.energy.ca.gov/reports/ reports_500.html 2. 2003 IceBank Performance Manual CALMAC. Chiller 1,600 1,400 1,200 1,000 Ice storage shortfall Stored cooling Tons 800 600 400 200 0 12 am 2 4 6 8 10 12pm 2 4 6 8 10 12 am Time of day Figure 3: Ice system loading with one chiller unavailable temperature reset, the building could be usable for most of a peak day and certainly all day for a non-design day. In a right-sized cooling system the equipment and ancillary components operate more efficiently at full load more often. So a right-sized partial ice storage design can provide similar safety factor and redundancy compared to conventional designs while improving efficiency, demand, connected load, and operating costs. Lowering operating costs can help earn LEED NC points in the Energy and Atmosphere section. Rightsizing with partial ice storage can reduce the impact of peak-time comfort cooling on the environment. A California study showed that power is generated and transmitted more efficiently at night, saving valuable natural resources. More efficient generation means lower greenhouse gas emissions as well. What about the installed cost? If there is room for ice tanks, the cost per ton is very similar. A chiller with a cooling tower or an air-cooled machine is about $450 per ton, which is very similar 44 Consulting-Specifying Engineer • AUGUST, 2007 http://www.energy.ca.gov/reports/reports_500.html http://www.energy.ca.gov/reports/reports_500.html

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - August 2007

Contents M/E Roundtable Giants 100 Pullout Poster Giants Stand Tall: CSE Giants 100 Report Electrical Design for Tall Buildings HVAC and Fire Safety for Elevator Systems How to Beat the Codes GAS Technology Supplement Recovering Waste Heat from Boilers New Applications for Tankless Water Heating Systmes Techniques Improve for Powder Coating MDF New Tools Available for Heat Treating Steel Direct Drive Engines

Consulting-Specifying Engineer - August 2007

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