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Date (5/3/2014). Selection and sizing of domestic hot water production and distribution. Havid El khaoui. Content. DHW demand House Apartment Buildings (central domestic hot water) Types of devices DHW production Dimensioning Recent developments. 3. 4. DHW- Demand.
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Selection and sizing of domestic hot water production and distribution Havid El khaoui
Content • DHW demand • House • Apartment Buildings (central domestic hot water) • Types of devices DHW production • Dimensioning • Recent developments 3
DHW- Demand • Large variation in flow rate: periods with little or no usage alternate with peak demands • Simultaneity i.f.v. the size of the building • Difference week <-> weekend • Graphs: • Flow (L/min) i.f.v. time • Cummulated volume i.f.v. time • Input for dimensioning • Peak flow (L / min) • Maximum daily consumption (L / day) L/min ∑ L
DHW- Demand-House Weekday:
DHW- Demand-House Weekend:
DHW- Demand- Apartment Building Weekend Weekday ∑ L @ 60°C ∑ L @ 60°C 277 appartements centrale DHW-production Uur (-)
DHW-production • Different types: • Instant production DHW is produced at time of DHW demand • Semi-instant • Semi-accumulation • Full accumulation (storage): DHW is produced before DHW demand and stored foto: I. Piette - ATIC
Instant gas water heater (house) • Open – closed (CO poisoning) • Ignition: pilot flame or turbine • Modulation (power control x% - 100%): • Hydraulic control • Thermal control
Instant gas water heater (house) • Modulation (power control x% - 100%): • Hydraulic (P ~ qDHW – assumes constant ∆ T) • Thermal (P ~ qDHW en TCW - important for solar energy) Minimum flow rate Minimum flow rate
Instant heater with CH (house) • Sometimes with limited accumulation • Limiting the waiting time • Less frequent startup • Lower power
Plate heat exchanger with boiler (apartment buildings) Boiler Heat exchanger DHW CW
Instantproduction No storage so less thermal losses lower investment less space With correct sizing: availability of an unlimited amount of hot water It must cover the DHW peak high power needed Sensitive to accumulation of lime stone (water softening) PRO’S CON’S
Accumulation • Ex: Electric boiler: low power to heat the total daily consumption at night rate
Accumulation Very good stability of the temperature = comfort Large peak flows possible with relatively limited capacity Takes large space in the building Major thermal losses Empty = Empty PRO’S CON’S
Semi-instant or semi-accumulation Storage Boiler Heat exchanger DHW CW Storage Boiler DHW CW Principe:
Semi-instant or semi-accumulation Smaller sizing Boiler Accumulation This system gives , if good dimensioned, a good temperature stability The power requirement is much less than instant production In comparison with full accumulation , still quite large boiler power required Requires more space than instant production Standby losses Pro’s Con’s
Semi-accumulation - Gas • With chimney or wall socket: • a closed unit • good insulation Illustraties: Ariston/Eole – ACV/Heatmaster
DHW-production Central Decentral
DHW-production Central Decentral • Decentral: • Pros: • No distribution net • Independent production Cons: • Multiple devices • large installed power • Multiple chimneys
DHW-production Central Decentral • Central: • Pros: • Low investment • Limited space needed • One chimney Cons: • High distribution losses • Difficult to devide the cost
Dimensioning Peak flow Foreign standards determine peak flow based on the taps in the installation: Used for sizing of pipes and instant DHW production
Nominal flow taps sum of all taps Dimensioning Peak flow Example: DIN 1988-300:2012 formula fordesign peak flow with coefficients (simultaneity!)
Dimensioning Peak flow
Dimensioning Peak flow Used for sizing: pipes For each section, a design peak flow is calculated -> pipe size instant DHW-production The needed power is calculated from the peak flow
Dimensioning Distribution (pipes) • The size of each pipe section is calculated from peak flow in the section, taking into account: • Available pressure after the water meter • Minium needed pressure at tap (typical 1 bar) • Pressure losses of height • Pressure losses: • Pipes (i.f.v. diameter) • Fittings (bends, tees, ...) • Appliances • Maximum pipe velocity (avoid noise)
Dimensioning Instant production • Pmin = qDHW,peak * c * (TDHW-TCW)/60.000 (kW) • With: • Pmin the minimum capacity of the water heater (kW) • qDHW,peak peak flow (L/min) • specific heat of water c = 4186 J / (kg.K) • for TCW is usually 10 ° C Example: Power needed for qDHW,peak = 9 L/min @ 60°C: Pmin = 9 * 4186 * (60-10)/60.000 = 31 kW
Dimensioning Maximum daily volume • DIN 4708: 50 L/day/person @ 45 °C = 35 L/dag @ 60°C • WTCB: 30 L/day/person @ 60 °C • Ecofys (NL) about : 25 - 50 l/day/person Bron: Ecofys Nl + diverse projecten in België
Cummulative used volume ( ∑ L) Heating ∆t heating Consumtion period (uur) 6 12 18 24 6 Dimensioning Accumulation Maximum daily volume
Dimensioning Accumulation • Volume accumulator: • Vacc= Vmax. day,DHW / f • With: • - Vacc en Vmax. day,DHW in L @ 60°C • f: tap efficienty accumulator - 0.9 voor 100 % accu’s • 0.8 voor boilers met ingebouwde ww Power accumulator: Pmin = Vacc * c * (TDHW-TCW) / ∆theating / 1000 (kW) With: • Δtheating time without use, available for heating accumulator (s) • specific heat of water c = 4186 J / (kg.K) • for TCW is usually 10 ° C taken
Dimensioning Accumulation • Example: • electric boiler for family of 5 on nightly rate • Vmax. day,DHW = 5 * 30 L = 150 L • Vacc, min = 150 L/ 0,9 = 167 L If: ∆theating = 6 u = 6*60 min*60 s = 21600 s • Pmin = 167 * 4186 * (60-10) / 21600 / 1000 = 1,6 kW
A Kitchen Living room B Bath room Bed room 1 Bed room 2 E C D Dimensioning Exercise: • 3 person appartment: • Select: • Pipe diameter • Power of Instant production • Power and Volume of Accumulation production
A Kitchen Living room B Bath room Bed room 1 Bed room 2 E C D Dimensioning Exercise: • 3 person appartment: • Select: • Pipe diameter • Power of Instant production • Power and Volume of Accumulation production
A 4m 2 B 1 E 1m D 3 C 1m 6 5 4 7 2m 2m 2m 1m 0,5m Dimensioning Exercise: • Isometric view • Select: • Pipe sections • Pipe distance • Exact location taps and production
Dimensioning Exercise: • Netherlands standard • Select: • The flow rate at each tap is given • Calculate the Tapping Unit at each tap • Calculate flow in each joint section • Simultaneity Q2 TU2 Q3 TU3 Q=(ΣTU)*0,083 Q1 TU1
2,25 TU 0,12 L/s 7 6 b 0,083 L/s 1 TU B-HOT 0,107 L/s 2TU 0,042 L/s 0,25 TU 3,25 TU 0,15 L/s 0,167 L/s 4 TU 0,167 L/s 4 TU 0,083 L/s 1 TU 0,042 L/s 0,25 TU B-COLD D E A a C 5 1 2 3 4 12,5 TU 0,29 L/s 8,5 TU 0,24 L/s 5,25 TU 0,19 L/s 1,25 TU 0,09 L/s Dimensioning Exercise: Netherlands standard Select:
Dimensioning Prod Spec Exercise: 2 • Netherlands standard • Select: • Calculate pipe sections 100kPa 1 • Pressure loss by height • Pressure loss by valve • Pressure loss by the pipe 3 rho*g*h/1000 200kPa ? 100kPa
Dimensioning Exercise: • Netherlands standard • Select: • Calculate pipe sections Rmax = pressure loss pipe (kPa/m) Pnet = supply pressure (kPa) Ptap = pressure needed at tap (kPa) ∆Ph = pressure loss by height (kPa) ∆Papp = pressure loss by valve (kPa) L = length route (m) f = factor for fittings
Dimensioning Exercise: • Netherlands standard • Select: • Calculate pipe sections Maximum speed (vmax) = 1,5 m/s Supply pressure (Psup) = 200 kPa Pressure at each tap (Ptap) = 100 kPa pressure loss by valve (∆Papp) = 50kPa Factor for fittings (f) = 1,2 Temperature cold (T) = 10°C Temperature hot (T) = 60°C Material = copper Mass density = 990 kg/m³ g = 9,81 m/s²
A 4m 2 B 1 E 1m D 3 C 1m 6 5 4 7 2m 2m 2m 1m 0,5m Dimensioning Exercise: • Netherlands standard • Select: • Calculate pipe sections L = Longest route and highest tap route D,hot = 9,5 m
A 4m 2 B 1 E 1m D 3 C 1m 6 5 4 7 2m 2m 2m 1m 0,5m Dimensioning Exercise: • Netherlands standard • Select: • Calculate pipe sections L = Longest route and highest tap route D,hot = 9,5 m route A,hot = 12,5 m
Dimensioning Exercise: • Netherlands standard • Select: • Calculate pipe sections Height of the tap
Dimensioning Exercise: • Netherlands standard • Select: • Calculate pipe sections
A 4m 2 B 1 E 1m D 3 C 1m 6 5 4 7 2m 2m 2m 1m 0,5m Dimensioning Exercise: • Netherlands standard • Select: • Calculate pipe sections
2,25 TU 0,12 L/s 6 7 13 10 13 10 8 b 0,083 L/s 1 TU B-HOT 0,107 L/s 2TU 0,042 L/s 0,25 TU A C D 0,167 L/s 4 TU B-COLD 0,167 L/s 4 TU 0,083 L/s 1 TU 0,042 L/s 0,25 TU a E 13 10 8 13 13 19,8 19,8 10 1 13 2 5 3 4 12,5 TU 0,29 L/s 8,5 TU 0,24 L/s 5,25 TU 0,19 L/s 1,25 TU 0,09 L/s Dimensioning Exercise: • Netherlands standard • Select: • Calculate pipe sections
Dimensioning Exercise: • Netherlands standard • Select: • Instant production • Pmin = qDHW,peak * ρ * c * (TDHW-TCW)/1.000 (kW) • With: • Pmin is the minimum capacity of the water heater (kW) • qDHW,peak peak flow at the water heater is 0,15 L/s @ 60°C • specific heat of water c = 4,19 kJ / (kg.K) • TDHW = 60 ° C • TCW = 10 ° C • mass density ρ = 980 (kg/m³) Pmin = 0,15 *980*4,19 * (60-10)/1.000 = 30 kW
Dimensioning Exercise: • Netherlands standard • Select: • accumulation production • Vacc = Vmax. day,DHW / f • Pmin = Vacc * ρ * c * (TDHW-TCW)/(1.000*∆theating) (kW) • With: • Vacc is the accumulator volume (L) • Vmax. day,DHW is the daily demand DHW per person per day (L) • Volume per person is 30L/day • F is the tap efficienty of the accumulator • Pmin the minimum capacity of the water heater (kW) • qDHW,peak peak flow at the water heater (L/s) • specific heat of water c = 4,19 kJ / (kg.K) • TDHW = 60 ° C &TCW = 10 ° C • mass density ρ = 980 (kg/m³) • Δtheating time available for heating accumulator (s)