PDF《Design Guide》

s total utility bill. The utility rates shown in Figure

1 for natural gas, electricity, water and sewer will be applied throughout this guide for cost estimating. Table 1. Typical hot water system cost for restaurants. Water Use (gal/d) Gas Use (therms/yr) Water/Sewer Cost* Gas Cost** Electricity Cost*** Annual Utility Cost Quick Service

500 1400 $2,000 $1,500 - $3,500 Full Service

2500 8800 $9,800 $9,700 $150 $19,650 California

2009 nominal utility rates: *$8.00/unit for water and sewer **$1.10/therm for natural gas ***$0.15/kWh for electricity (recirculation pump) Figure 1. Average California utility rates for restaurants in 2010. Improving Hot Water System Performance Design Guide C Energy Efficient Water Heating, Delivery and Use C 3.26.10

3 Fundamentals Conventional hot water systems are comprised of three fundamental component groups: water heater(s) with or without storage, distribution piping, and an array of hot water-using appliances and faucets. In advanced systems, a fourth component is added upstream the water heater to pre-heat the supply water using waste heat or solar. This guide will only briefly touch on free heating technologies as more research, development and demonstration projects are needed for a better understanding of the design parameters and economics. Most water heaters installed in restaurants are storage (or tank) type units designed to hold water at a preset temperature until it is needed. A small number of larger foodservice facilities use a boiler with an external storage tank. A growing number of operations, particularly quick-service restaurants, have entertained tankless water heaters. The dominant energy source for heating water in California foodservice facilities is natural gas, followed distantly by electric resistance and propane. Distribution systems consist of a network of piping, preferably wrapped in insulation to reduce heat loss. In moderate to large systems (e.g., full-service restaurants), a recirculation loop and pump are installed to maintain hot water in the supply lines for faster delivery of hot water to appliances and faucets. Otherwise, it literally can take minutes for hot water to arrive at its intended temperature at important fixtures such as hand-washing sinks and dishwashers, jeopardizing proper sanitation. In food service, the hot water system is designed to deliver water at temperatures typically ranging between 120°F and 140°F to faucets and equipment. An exception is hand sinks where the water temperature may be reduced to 100°F. Point-of-use equipment includes fixtures such as faucets, pre-rinse spray valves, and dishwashers. The use of this equipment varies throughout the work day, but peaks typically during the lunch and dinner rush. End-of-day cleaning of the facility and associated use of a mop sink for filling buckets or attaching a hose for wash down can be a major hot water draw. Glossary of Abbreviations, Conversions and Terms Abbreviations FSTC C Food Service Technology Center HCF (or CCF) C

100 cubic feet gph C gallons per hour gpm C gallons per minute gpr C gallons per rack psi C pounds per square inch Conversions

1 Therm =

100 kBtu = 100,000 Btu

1 unit of water =

1 HCF =

748 gallons

1 acre-feet = 325,851 gallons Terms British thermal unit (Btu) is the energy required to raise the temperature of

1 lb of water 1°F. Btu/h is a unit of power, it also describes the power or maximum input rating of water heaters. Installed cost encompasses capital, labor and installation cost of a project or the final cost installed. kWh or kilowatt-hour is used to express the energy delivered or used and is the product of power in kilowatts multiplied by time in hours. Latent heat of vaporization is the heat released when water vapor condenses back to a liquid onto a surface, the latent energy absorbed during evaporation [during the gas combustion process] is released as heat onto the [heat exchanger] surface. Recovery rate is the number of gallons of water the storage water heater can bring to temperature per hour and it is a function of temperature rise (output temperature C inlet temperature). R-value is a measure of thermal resistance, the bigger the number, the better the insulation'