State Water Heaters 317913-000 Скачать руководство пользователя | Manualshive

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5

Hot Water Demand

The major determination in sizing and the basis of all computations is establishing the probable demand
for hot water. In addition, any unusual conditions which might relate to hot water consumption must
also be recognized and planned for. Unusual conditions will be described under Profiles of Operation.

Sources of hot water demand information include the ASHRAE (American Society of Heating,
Refrigerating and Air Conditioning Engineers) Guide, and hot water using equipment manufacturers
such as dishwasher and washing machine makers. Government agencies may also require demand
criteria be met.

Profiles of Operation

The system designer should draw a profile of the proposed system hot water usage demand period.
The profile will also include the recovery period available before the next demand. Demand and
recovery periods can be measured in seconds, minutes or hours.

Any unusual needs for hot water during the demand or recovery periods are identified in order to
provide additional tank and/or recovery capacity. An unusual need could be a lesser, but significant
hot water requirement appearing just after the demand period. For example, a motel could have a
laundry operation which begins in mid-morning, after the guest shower load is over. If not taken into
consideration there many be no hot water available for the washing machines.

An oversimplification of system design is to say that systems are either for intermittent use or continuous
use as shown in the following profiles.

.

This example shows two demand and recovery periods within a day.

•

A combination of heater recovery and hot water storage capacity should be selected to handle the
demands.

•

The demands are separated by an 8 and a 12 hour recovery period.

•

The heater recovery capacity of the shortest recovery period must be sufficient to heat all the water
in storage.

•

Short demands usually mean placing emphasis on tank size. Heater recovery capacity is emphasized
on longer demands.

•

The dividing line between long and short demands is about 3 to 4 hours.

•

In this example storage is most important.

-The purpose of the storage tank is to permit relatively low heater recovery capacity while still

maintaining adequate hot water supply during the demand period.

II.

Principles of Sizing

Intermittent Use Profile

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Содержание 317913-000

Страница 1: ...Printed in the U S A 0210 317913 000 A TECHNICAL GUIDE TO DESIGNING ENERGY EFFICIENT COMMERCIAL WATER HEATER SYSTEMS ...

Страница 2: ...em 13 Sizing Without Prepared Information 13 14 One Temperature System 14 Two Temperature System 15 Field Assistance 15 This guide is different than most produced by the water heating industry Instead of just referring you to prepared sizing information the guide shows you how it s done Then when new model heaters are Index Foreword introduced or applications are different you will have the inform...

Страница 3: ...ded as more heat is added the water becomes hotter This water temperature guide shows typical water heating system design temperatures In practice the system designer will establish the temperature or temperatures of hot water needed for the various activities through consultation with the user or their representative It is also necessary for the system designer to know the coldest entering water ...

Страница 4: ...er supplier High water supply pressure above the rated working pressure of the heater should be reduced by a water pressure reducing valve set to about 50 psig This will also reduce water consumption but more important will bring the water pressure well within the working pressure range of the heater It is then possible to provide proper relief valve protection on the heater It is also necessary t...

Страница 5: ... Air Conditioning Engineers Guide and hot water using equipment manufacturers such as dishwasher and washing machine makers Government agencies may also require demand criteria be met Profiles of Operation The system designer should draw a profile of the proposed system hot water usage demand period The profile will also include the recovery period available before the next demand Demand and recov...

Страница 6: ... in order to select a heater model In this example heater recovery is most important as the system for all practical purposes is an instantaneous one That is it heats the water at the rate it is being used If a tank type water heater is used the tank size is minimum just large enough to put the heat into the water Recovery Capacity Tables Recovery capacity tables are the published results of labor...

Страница 7: ...cannot be replenished until the recovery capacity of the heater exceeds the demand upon the system This is usually after the peak hot water demand period has ended Obviously the actual availability and temperature drop of any system will depend upon the hot water demand flow rate and piping concept The potential for hot water temperature drop during the demand period must be kept in mind by the sy...

Страница 8: ...tank size would be 70 0 7 100 gallons Note Storing water below 140 F may require more storage capacity If the input of the heater is satisfactory for recovery purposes but the tank size is not an auxiliary hot water storage tank may be piped into the system to increase the amount of available hot water during the demand period State instruction manuals show the details Electric Tank Type Heaters U...

Страница 9: ...t 25 minutes 70 0 171 41 hour Select minimum recovery and maximum storage if the hot water demand period is less than 3 or 4 hours Heater recovery must be sufficient to reheat the entire tank contents before the next demand period To summarize Short Demand Long Demand Min recovery Max recovery Max storage Min storage Check for the possibility of any hot water needs occurring during the recovery pe...

Страница 10: ... on a demand rate basis This means in addition to the energy charge measured in kWh there is a charge for the demand measured in kW that a customer imposes upon the electrical service Your power company will provide and explain rate information upon request kWh ENERGYUSED HEATS WATER COSTS PENNIES kW DEMAND DOESN T HEAT WATER COSTS DOLLARS The presence of a demand rate means the system designer sh...

Страница 11: ...ssible operating costs Electricity is an example of a fuel which must be applied thoughtfully to avoid unnecessary demand charges 4 Provide the quality and features needed to attain the desired results at least cost Least cost means not only initial cost but operating costs as well Often times higher initial cost can be offset by lower operating costs achieved by using State energy saving water he...

Страница 12: ...01 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12345678901 12 2 Two Temperature provides two temperature hot water service by means of a water mixing valve or through a pre heater booster heater combination In the first concept the heater storage tank is maintained at the highest system ...

Страница 13: ...he following chart summarizes the responsibilities for each of the roles Remember your customer s success or profit may depend upon the continued availability of hot water and you will achieve that goal through proper system selection and sizing IDENTITY RESPONSIBILITY Customer Must define his needs System designer Designs a water heating system to satisfy the customer s needs Acts as an interface...

Страница 14: ...ry and storage as necessary see page 10 8 Divide the heater tank size by the heater recovery to be certain the tank will be recovered by the time of the next demand If not adjust recovery and storage as necessary see page 10 1 The demand could be in minutes or seconds In either case all references to hours in the procedure would revert to minutes or seconds For example a stationary rack type dishw...

Страница 15: ...requirement by 1 4 in 100 F temperature rise applications a This means 1 4 more water can be raised from 40 F to 140 F than 40 F to 180 F with the same amount of energy b Multiplier formula Hot Cold multiplier Mixed Cold Example 180 40 140 1 4 140 40 100 c 75 gallons 180 F water required x 1 4 105 equivalent gallons of 140 F water Add the converted 180 F water requirement to the 140 F requirement ...

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