SIZING OF WATER HEATERS

SIZING OF WATER HEATERSWATER HEATINGWater heating is a thermodynamic process using an energy source to heat water above its initial temperature.

TRADITIONAL WATER HEATERS Kettle cauldron

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.

TYPES OF WATER HEATERSConventional or storage water heaterSolar water heaterStorage and heat pump water heaterOn-demand or tankless or instataneous water heaterPool water heaterConventional or Storage Water Heater Electric Gas-fired Oil-fired

Solar Water Heater Passive Type with Active Type withEvacuated Tube Collector Flat-plate Collector

Storage and Heat Pump Water Heater Storage tank Heat pump

On-demand or tankless or Instataneous Water Heater Single Point Multi-point

Pool Water Heater Electric Solar

Before buying a new water heater,you need to consider the following:

1. Size or FHR (First Hour Rating)2. Energy efficiency3. Fuel type and availability4. Costs

IMPT. FACTORS OF WATER HEATERThe Energy FactorEnergy 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 themselves through a lifetime of energy savings.

First Hour RatingAnother important factor in choosing a water heater. The 1st Hour Rating is an indicator of how much hot water a particular model can provide. The rating, in gallons of usable (desired temperature) hot water is reached by combining the amount of usable hot water stored in the tank plus how many gallons of usable hot water the water heater can generate in one hour of operation. For example, if a 40-gallon natural gas water heater will store 31 gallons of usable hot water and can deliver 41 gallons of usable hot water in the first hour, its 1st Hour Rating is 72 gallons. 1st Hour Ratings are included in the Energy Factor charts.

ENERGY SOURCES FOR HEATING WATERNatural gas or liquefied petroleum gasOil or solid fuelsElectricitySolar energyHeat pumpsHot water heat recyclingGeothermal heatingWATER HEATING IN SOME COUNTRIESGeothermal heating and hot water heat recycling

SIZING OF STORAGE WATER HEATER Basic Equation:Q = W x cp x tWhere:Q = time rated heat transfer, Btu/hrW = 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

The British thermal unit (BTU or Btu) is a traditional unit of energy. It is approximately the amount of energy needed to heat one pound of water one degree Fahrenheit. One Btu is equal to about 1.06 kilojoules. It is used in the power, steam generation, heating and air-conditioning industries.

Farenheit/Celsius Convertion Formula:C = (F 32) x 5/9 F = C x 9/5 + 32SAMPLE PROBLEM Design the water heater of a 4-storey hotel with 60 guestrooms.

SOLUTION:Hot water loads of a hotel1. Guest rooms demand2. Food service demand 3. Laundry demand

ASSUMPTIONS:Number of Person per Room:Convention hotel 1.5 person/roomBusiness/travellers hotel 1.5 person/roomGeneral occupancy hotel 2 person/roomPeak Demand Period:Convention hotel 1 hour peakBusiness/travellers hotel 1 hour peakGeneral occupancy hotel 2 hours peak

GIVEN:no. of guestroom60 roomsno. of person/room1.5 (assumed)% of guests shower atpeak time70% (assumed)ave. shower time5 min (assumed)max. flow of shower2.5 gpmsupply water temp68 F or 20Chot water temp105 F or 40.5CNote: hot water to be stored at 140F or 60Cand delivered to guest room at 105F or 40.5CCOMPUTATION 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 hourVol. of hot water = 63 x 5min/guest x 2.5gpm = 787 gal of 105F at peakSince stored water is 140F; equivalent volume isVol = (105 68) x 787 gal = 364 gal (140 68)Q = 364gal/hr x 8.33lb/gal x 1Btu/lbF x (140-68)F = 218,313 Btu/hrIf Energy Factor of Water Heater is 0.90 thenQ = 218,313 = 242,570 Btu/hr0.90

In KW: 242,570 Btu/hr = 71 KW 3,413 Btu/KW.hrProperly size supply and recirculation system isnecessary for efficient and economical operation

Over sizing the system will cause increased installation costs for equipment and materials, and create additional heat losses, lessening efficiency.

Under sizing the system will seriously hamper effective circulation, which means adequate hot water will not be available at all fixtures.SIMPLE METHOD FOR SIZING RECIRCULATING PUMPS 1 gpm for 20 fixtures units0.5 gpm for each or 1 riser1 gpm for each 1 or 1 riser2 gpm for each 2 riser

SIZING OF SOLAR WATER HEATERFACTORS OF SOLAR WATER HEATER:1. Economics 2. Geographic location and solar resource3. Correct system size4. Building structure

ACTIVE SOLAR WATER HEATER:- Storage tank as per requirement per day- 1.5 gal per square foot of collector

SIZING OF SOLAR WATER HEATERPASSIVE SOLAR WATER HEATER:Storage Tank: 30 gal cap 1 to 2 persons 60 gal cap 2 to 3 persons80 gal cap 3 to 4 personsCollector Area for Tropical Countries:- 20 ft for first two family members- add 8 ft for each additional familymembers

COMPUTATION FOR SOLAR WATER HEATER:Total no. of guests = 60 rms x 1.5 guest/room = 90 guestsVol. of hot water = 90 x 5min/guest x 2.5gpm = 1,125 gal of 105F at peakSince stored water is 140F; equivalent volume isVol = (105 68) x 1,125 gal = 578 gal (140 68)Collector Area = 578 gal = 385 ft 1.5gal/ftSIZING OF HEAT PUMP WATER HEATERHeat pump water heaters require installation in locations that remain in the 40F 90F (4.4C 32.2C) range year-round and provide at least 1,000 cubic feet (28.3 cubic meters) of air space around the water heater.

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

COMPUTATION FOR SOLAR WATER HEATER:Total no. of guests = 60 rms x 1.5 guest/room = 90 guestsVol. of hot water = 90 x 5min/guest x 2.5gpm = 1,125 gal of 105F at peakSince 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

FACTORS OF DEMAND (TANKLESS OR INSTANTANEOUS) WATER HEATERAdvantages of Tankless:Continuous hot waterUses energy only when hot water is demandedLower energy costs (11% - 60% energy savings)Designed to last 20 yearsSmaller than hot water tank units, saving floor space

FACTORS OF DEMAND (TANKLESS OR INSTANTANEOUS) WATER HEATERDisadvantages of Tankless:Must size the unit correctly to avoid losing hot waterMay need more than one tankless unit to heat water for more than one showerMore 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 sizeNeed to be serviced periodically (to clean scale build-up)More complex/difficult to service than standard water heaterSIZING OF DEMAND (TANKLESS OR INSTANTANEOUS) WATER HEATERDemand (tankless or instataneous) water heaters are rated by the maximum temperature rise possible at a given flow rate. Therefore, to size a demand water heater, you need to determine the flow rate and the temperature rise youll need for its application (whole house or a remote application, such as just a bathroom) in your home.

SIZING OF DEMAND (TANKLESS OR INSTANTANEOUS) WATER HEATERTypically, a 70F (39C) water temperature rise is possible 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 flow rates, install low-flow water fixtures.

ARISTON INSTANTANEOUS WATER HEATER SPECIFICATIONSpecifications GL 2.5 GL4 GL6 PLUSTank Volume 2.5 Gallons 4 Gallons 6 GallonsDimensions 14x14x 10" 14x14x12 17x17x 14Recovery at 8 GPH* 10.5 GPH* 12.5 GPH* 90F Rise Water Connections inch NPT inch NPT inch NPTRelief 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

MOST INSTANTANEOUS WATER HEATER SPECIFICATIONPower 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/galQ = 49.82 gal/hr = 0.83 gpm 60min/hr SIZING A GAS OR HEAT PUMP SWIMMING POOL HEATERGas 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, 5 hp/100,000 Btu, and 6 hp/125,000 Btu.

Calculating Approximate SizeDetermine your desired swimming pool temperature.Determine the average temperature for the coldest month of pool use.Subtract the average temperature for the coldest month from the desired pool temperature. This will give you the temperature rise needed.Calculate the pool surface area in square feet.Use the following formula to determine the Btu/hour output requirement of the heater:

Btu/Hr = Pool Area x Temp Rise x 12This 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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