Domestic Hot Water Systems: Heat Sources, Methods, Systems, & Distribution

  

PAUL HAY Capital Projects

www.phcjam.com

Hot Water Systems

Author:            Paul Hay

e-mail:              paul.hay@phcjam.com

profile:             www.linkedin.com/in/phcjam

1.0       INTRODUCTION TO HOT WATER SYSTEMS

1.1       Domestic Hot Water (DHW) is needed for comfort and a degree of sterilization particularly in Laundries and Kitchens.

1.2       In Jamaica, the need for hot water is greatest in hotels, hospitals, pharmaceutical manufacturing and food processing facilities.

1.3       DHW Systems vary depending on (a) heat source, (b) Method of heating water, (c) local versus central equipment and (d) respective distribution trees.

2.0       HEAT SOURCES

2.1       Solar Energy is the only renewable source of energy used.

2.2       Natural gas and electricity are also used as energy sources.

2.3       Otherwise, heat-recovery devises can be used to heat water.

3.0       METHODS OF HEATING

3.1       Water is heated to a maximum temperature of 60 deg. C.

3.2       On-demand heaters do not use no storage tanks:

            3.2.1   Heaters rapidly heat water to the desired temperature and immediately distributes it;

            3.2.2   Heater capacity is equivalent to the peak demand.

3.3       Storage tanks hold approximately one-third the daily cold water consumption:

            3.3.1   A pressure-relief valve is placed on storage tanks as a safeguard against excess temperature and pressure.

            3.3.2   Direct heating involves (a) the use of submersible electrical heating elements, or (b) water is first passed through coils which are subsequently heated by solar radiation, fire, or hot gases;

         3.3.3   Indirect heating involves (a) the use of heat-extracting devices, such as incinerators, not primarily meant to heat water, or (b) passing steam or hot liquids through submerged heating coils.

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Figure 1: Recommended Capacity of Hot Water Tanks [source:- Journal of Light Construction Field Guide (vol. 2)]

4.0       LOCAL & CENTRAL SYSTEMS

4.1       Local systems are recommended where distance between areas of use exceed 15 m;

4.2       Central systems should be located nearest to fixtures which utilize the most hot water (eg. dish-washers and washing machines.)

Figure 2: Central Hot Water Distribution [source:- Journal of Light Construction Field Guide (vol. 2)]

5.0       DISTRIBUTION TREES

5.1       EEBC-94 requires all exposed piping and storage tanks to be insulated.

5.2       A check valve is located on the cold water intake pipe to prevent hot water entering the cold water distribution tree.

5.3       If hot water storage tanks are located indoors, the pressure relief valve should be connected to a drain.

5.4       A non-circulating system has a distribution tree directly from the heater to individual plumbing fixtures.

5.5       A circulating system has a return line to the heater:

            5.5.1   This system is used in large residences or systems;

            5.5.2   Time for delivery of hot water to fixtures is reduced;

            5.5.3   A circulating pump can be used for constant supply of hot water.

6.0       INSTALLATION

6.1       Gas-burning equipment should be installed in well ventilated areas.

6.2       Exposed open-flame equipment should not be installed in bedrooms, enclosed garages, or rooms primarily intended for storage.

6.3       Where more than one fixture is supplied by a single gas line, each fixture shall receive an independent lock-off valve.

6.4       Equipment should be accessible for servicing and repair.

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FURTHER READING

Mechanical and Electrical Equipment for Buildings, Benjamin Stein & John S. Reynolds, John Wiley & Sons Inc., U.S.A.

Construction Materials & Processes, Don G. Watson, McGraw-Hill Book Co., USA.

                        Jamaica Energy Efficiency Building Code [EEBC-94], Jamaica Bureau of Standards