Sizing of Water Heaters

7/30/2019 Sizing of Water Heaters

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SIZING OF

WATER

HEATERS


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Randy L. AmanCivil EngineerRegistered Master PlumberReal Estate Broker

PSPE National Auditor

PSPE Camarines Chapter President 2008

NAMPAP National Director 2004 & 2006NAMPAP Camarines Naga City Chapter President

2003

PICE Naga City Chapter President 2004


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WATER HEATING

Water heatingis a thermodynamic processusing an energy source to heat water aboveits initial temperature.

Typical domestic uses of hot water are forcooking, cleaning and bathing.

Domestically, water is traditionally heated invessels known as kettles, cauldrons and pots.


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TRADITIONAL WATER HEATERS

Kettle cauldron pot
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In industry, both hot water and water heated to

steam have many uses.

Appliances for providing a more-or-less

constant supply of hot water are variously

known as water heaters, boilers, heat

exchangers, calorifiers, or geysers.

These are Mechanical Engineers task.


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TYPES OF WATER HEATERS

1. Conventional or storage water heater

2. Solar water heater

3. Storage and heat pump water heater

4. On-demand or tankless or instataneous

water heater5. Pool water heater


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Conventional or Storage Water Heater

Electric Gas-fired Oil-fired


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Solar Water Heater

Passive Type with Active Type with

Evacuated Tube Collector Flat-plate Collector


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Storage and Heat Pump Water Heater

Storage tank Heat pump


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On-demand or tankless or

Instataneous Water Heater

Single Point Multi-point


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Pool Water Heater

Electric Solar
http://www.solar-pool-heaters.us/1-468240-B000A4WPVS-Sunheater_Solar_Pool_Heating_System_Above_Ground_Pool_System_421A.html


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Before buying a new water heater,

you need to consider the following:

1. Size or FHR (First Hour Rating)2. Energy efficiency

3. Fuel type and availability

4. Costs
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12800http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12800http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12800http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12800http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12800http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12800


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IMPT. FACTORS OF WATER HEATER

The Energy Factor

Energy Factor (EF) is an overall efficiency

rating of the water heater. The higher the EF,

the more efficient the model. Water heaters

with high EF ratings may cost more initially

but save energy and money in the long run.

Eventually, they will pay for themselvesthrough a lifetime of energy savings.


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First Hour RatingAnother important factor in choosing a water heater.

The 1st Hour Rating is an indicator of how much hotwater a particular model can provide. The rating, ingallons of usable (desired temperature) hot water isreached by combining the amount of usable hotwater stored in the tank plus how many gallons ofusable hot water the water heater can generate inone hour of operation. For example, if a 40-gallonnatural gas water heater will store 31 gallons ofusable hot water and can deliver 41 gallons of usablehot water in the first hour, its 1st Hour Rating is 72gallons. 1st Hour Ratings are included in the EnergyFactor charts.


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ENERGY SOURCES FOR HEATING WATER

Natural gas or liquefied petroleum gas

Oil or solid fuels

Electricity

Solar energy

Heat pumps

Hot water heat recycling Geothermal heating


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WATER HEATING IN SOME COUNTRIES

Geothermal heating and hot water heat recycling
http://en.wikipedia.org/wiki/File:Hot_water_heat_recycling_unit.jpg


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SIZING OF STORAGE WATER HEATER

Basic Equation:

Q = W x cp xt

Where:

Q = time rated heat transfer, Btu/hr

W = weight of heated water, lbs/hrcp = specific heat of water at standard

condition, say 1 Btu/lbF

t = change of heated temp of water F
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12800http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12800


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The British thermal unit(BTU or Btu) is a

traditional unit of energy. It is approximately

the amount of energy needed to heat onepound of water one degree Fahrenheit. One

Btu is equal to about 1.06 kilojoules. It is used

in the power, steam generation, heating andair-conditioning industries.

Farenheit/Celsius Convertion Formula:C = (F 32) x 5/9 F = C x 9/5 + 32


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SAMPLE PROBLEM

Design the water heater of a 4-storeyhotel with 60 guestrooms.

SOLUTION:Hot water loads of a hotel

1. Guest rooms demand

2. Food service demand3. Laundry demand
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ASSUMPTIONS:

Number of Person per Room:

Convention hotel 1.5 person/room

Business/travellers hotel 1.5 person/room

General occupancy hotel 2 person/room

Peak Demand Period:

Convention hotel 1 hour peak

Business/travellers hotel 1 hour peakGeneral occupancy hotel 2 hours peak


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GIVEN:

no. of guestroom 60 rooms

no. of person/room 1.5 (assumed)

% of guests shower at

peak time 70% (assumed)

ave. shower time 5 min (assumed)

max. flow of shower 2.5 gpm

supply water temp 68 F or 20C

hot water temp 105 F or 40.5C

Note: hot water to be stored at 140F or 60C

and delivered to guest room at 105F or 40.5C


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COMPUTATION FOR STORAGE WATER HEATER:

Total no. of guests = 60 rms x 1.5 guest/room

= 90 guests

% of guests showering per hour = 90 x 0.70

= 63 guests per hour

Vol. of hot water = 63 x 5min/guest x 2.5gpm

= 787 gal of 105F at peak

Since stored water is 140F; equivalent volume isVol = (105 68) x 787 gal = 364 gal

(140 68)


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Q = 364gal/hr x 8.33lb/gal x 1Btu/lbF x (140-68)F

= 218,313 Btu/hr

If Energy Factor of Water Heater is 0.90 then

Q = 218,313 = 242,570 Btu/hr

0.90

In KW: 242,570 Btu/hr = 71 KW3,413 Btu/KW.hr


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Properly size supply and recirculation system is

necessary for efficient and economical operation

Over sizing the system will cause increased

installation costs for equipment and materials,

and create additional heat losses, lesseningefficiency.

Under sizing the system will seriously hampereffective circulation, which means adequate

hot water will not be available at all fixtures.


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SIMPLE METHOD FOR SIZING

RECIRCULATING PUMPS

1 gpm for 20 fixtures units

0.5 gpm for each or 1 riser

1 gpm for each 1 or 1 riser

2 gpm for each 2 riser


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SIZING OF SOLAR WATER HEATERFACTORS OF SOLAR WATER HEATER:

1. Economics

2. Geographic location and solar resource

3. Correct system size

4. Building structure

ACTIVE SOLAR WATER HEATER:

- Storage tank as per requirement per day

- 1.5 gal per square foot of collector


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SIZING OF SOLAR WATER

HEATER

PASSIVE SOLAR WATER HEATER:

Storage Tank:

30 gal cap 1 to 2 persons60 gal cap 2 to 3 persons

80 gal cap 3 to 4 persons

Collector Area for Tropical Countries:

- 20 ft for first two family members- add 8 ft for each additional family

members


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COMPUTATION FOR SOLAR WATER HEATER:


= 90 guests

Vol. of hot water = 90 x 5min/guest x 2.5gpm

= 1,125 gal of 105F at peak

Since stored water is 140F; equivalent volume is

Vol = (105 68) x 1,125 gal = 578 gal

(140 68)Collector Area = 578 gal = 385 ft

1.5gal/ft


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SIZING OF HEAT PUMP WATER HEATER

Heat pump water heaters require installation inlocations that remain in the 40F 90F(4.4C 32.2C) range year-round andprovide at least 1,000 cubic feet (28.3 cubic

meters) of air space around the water heater.

In sizing the water heat pump requirement, usethe Btu/hr or kW capacity of the water heatpump but do not use the peak load alone,use a whole day hot water requirement.

COMPUTATION FOR SOLAR WATER HEATER


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COMPUTATION FOR SOLAR WATER HEATER:


= 90 guestsVol. of hot water = 90 x 5min/guest x 2.5gpm

= 1,125 gal of 105F at peak

Since stored water is 140F; equivalent volume isVol = (105 68) x 1,125 gal = 578 gal

(140 68)

Q = 578gal/hr x 8.33lb/gal x 1Btu/lbF x (140-68)FQ = 346,661 Btu/hr

In KW: 346,661 Btu/hr = 101 KW

3,413 Btu/KW.hr


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FACTORS OF DEMAND (TANKLESS OR

INSTANTANEOUS) WATER HEATER

Advantages of Tankless:Continuous hot water

Uses energy only when hot water is

demanded

Lower energy costs (11% - 60% energy

savings)

Designed to last 20 years

Smaller than hot water tank units, saving

floor space


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FACTORS OF DEMAND (TANKLESS OR


Disadvantages of Tankless: Must size the unit correctly to avoid losing hot water

May need more than one tankless unit to heat water for

more than one shower

More expensive than hot water tank units

May need to limit the flow of water to properly heat

water (for example, to fill a tub)

Existing gas and water lines may need to be increased in

size

Need to be serviced periodically (to clean scale build-up)

More complex/difficult to service than standard water

heater


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SIZING OF DEMAND (TANKLESS OR


Demand (tankless or instataneous) waterheaters are rated by the maximumtemperature rise possible at a given flowrate. Therefore, to size a demand waterheater, you need to determine the flow rateand the temperature rise youll need for itsapplication (whole house or a remote

application, such as just a bathroom) in yourhome.


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SIZING OF DEMAND (TANKLESS OR


Typically, a 70F (39C) water temperature rise ispossible at a flow rate of 5 gallons per minute

through gas-fired demand water heaters and 2

gallons per minute through electric ones.Faster flow rates or cooler inlet temperatures

can sometimes reduce the water temperature

at the most distant faucet.To reduce flowrates, install low-flow water fixtures.


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ARISTON INSTANTANEOUS WATER HEATER SPECIFICATION

Specifications GL 2.5 GL4 GL6 PLUS

Tank Volume 2.5 Gallons 4 Gallons 6 GallonsDimensions 14x14x 10" 14x14x12 17x17x 14

Recovery at 8 GPH* 10.5 GPH* 12.5 GPH*

90F RiseWaterConnections inch NPT inch NPT inch NPT

Relief Valve installed installed included*Gallons Per Hour - First Hour Recovery

All Units:Voltage 110/120 Volts Phase Single Amperage

12.5 amps Temperatures 65 - 145F Heating Capacity

1500 Watts Operating Pressure 150 psi


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MOST INSTANTANEOUS WATER HEATER SPECIFICATION

Power Rating = 4,500W or 4.5kW

Convert kW to Btu/hr = 4.5 x 3,413 = 15,358.5 Btu/hr

Q = W x cp x t

then W = Q = 15,358.5_

cp x t 1 x (105 -68)

Q = 415 lbs = __415 lbs/hr_ = 49.82 gal/hr

8.33lbs/gal

Q = 49.82 gal/hr = 0.83 gpm

60min/hr


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SIZING A GAS OR HEAT PUMP

SWIMMING POOL HEATER

Gas pool heaters are rated by Btu (British

thermal unit) output. Outputs range from

75,000 Btu to 450,000 Btu.

Heat pump pool heaters are rated by Btu

output and horsepower (hp). Standard

sizes include 3.5 hp/75,000 Btu, 5hp/100,000 Btu, and 6 hp/125,000 Btu.


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Calculating Approximate Size Determine your desired swimming pool

temperature. Determine the average temperature for the

coldest month of pool use.

Subtract the average temperature for thecoldest month from the desired pooltemperature. This will give you the temperaturerise needed.

Calculate the pool surface area in square feet. Use the following formula to determine the

Btu/hour output requirement of the heater:


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Btu/Hr = Pool Area x Temp Rise x 12

This formula is based on 1 to 1.25F

temperature rise per hour and a 3.5

mile per hour average wind at the

pool surface. For a 1.5F rise multiply

by 1.5. For a 2F rise multiply by 2.0.


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Thank you

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Sizing of Water Heaters