1/54

Circulation pump, safety valve,

expansion vessel

pressure loss

efficiency of pump

secured heat output

safety valve sizing

expansion vessel sizing

2/54

Circulation pump

similar principle as for heating system

flowrate

according to collector area (specific flowrate l/h.m2)

regime (high-flow, low-flow, according to collector producer)

calculation of pressure loss of collector loop

influence of heat transfer fluid properties (viscosity, density)

low consumption of electricity for pump in operation

working point in the area of high efficiency of pump

circulators with permanent magnets

3/54

Pressure loss calculation

friction loss

local loss (valves, fittings, etc.)

loss of components (collector field, heat exchanger)

determination of reference working point P

flowrate of fluid (according to collector area)

pressure loss for considered temperature (20 °C, 80 °C)

selection of pump

4/54

friction coefficient l

laminar flow

l = 64/Re

turbulent flow for hydraulic smooth pipes (Blasius)

Friction loss

ll 2

2w

d

lp

calculation, diagram

4 Re

316,0l

5/54

Friction loss

6/54

Viscosity of propylenglycol

0

1

2

3

4

5

6

7

20 40 60 80 100

t [°C]

[mm2/s]

propylenglykol+voda

voda

7/54

problematic determination of coefficient for local loss in laminar

flow zone

available only tables for developed turbulent flow

simplified calculation 0.3 x friction loss

Local loss

l 2

2wp

8/54

0

2 000

4 000

6 000

8 000

10 000

0 25 50 75 100 125 150 175 200

V [l/h]

p [Pa]

S

M

Z T

Pressure loss of solar collectors

9/54

Working point

0

2

4

6

8

0 2 4 6 8

průtok [m3/h]

dis

po

zičn

í tla

k [m

]

20 °C

80 °C

field of maximum efficiency

flowrate [m3/h]

disc

harg

e pr

essu

re (

tota

l hea

d]

[m]

10/54

Efficiency of pump

consumption of electricity by solar system

consumption of primary energy x savings of primary energy

efficiency of electricity production 35 %

effort to reduce electricity consumption

efficiency of circulator (conversion of electricity to mechanical

energy)

eee

č

P

Vp

P

VY

P

P

11/54

Efficiency of pump

0

1

2

3

4

5

0 5 10 15 20 25

V [m3/h]

H [m]

0

0,1

0,2

0,3

0,4

0,5

účinnost

H - V

účinnost efficiencyefficiency

water

propylenglycol/water

12/54

Efficiency of pump

0,0

0,1

0,2

0,3

0,4

0,5

0,0 1,0 2,0 3,0V [m

3/h]

účinnost

0,0

0,1

0,2

0,3

0,4

0,5

0 10 20 30V [m

3/h]

účinnost

in maximum efficiency point eta = 5 to 15 %

real operation: < 5 %

small systems: effectivity is low

efficiencyefficiency

13/54

Hydraulic stations

simplification of installation

circulation pump

valves

check valve

connection for expansion vessel

safety valve

themometers

attention: circulation pump could be significantly oversized !

14/54

Hydraulic stations

15/54

Electricity consumption

annual electricity need

volume flowrate

pressure loss of collector loop

hydraulic power

efficiency of circulation pump

power input of pump

typical annual operation period 2000 h

calculation for typical operation point tm = 40 °C

16/54

Pressure loss calculation

low flow

velocity w = 0.4 m/s

Reynolds number Re = 3183

friction coefficient l = 0.02 (laminar flow) 0.042 (turbulent)

friction loss pl = 17 000 Pa

local loss pm = 0.3 * pl = 5 600 Pa

pressure loss of heat exchanger 3000 Pa (450 l/h)

pressure loss of collectors 2000 Pa (balance valves)

total: 27 600 Pa

17/54

Pressure loss calculation

high flow

velocity w = 0.6 m/s

Reynolds number Re = 9593

friction coefficient l = 0.032 (turbulent)

friction loss pl = 15 600 Pa

local loss pm = 0.3 * pl = 5 200 Pa

pressure loss of heat exchanger 6000 Pa (2600 l/h)

pressure loss of collectors 2000 Pa (balance valves)

total: 28 800 Pa

18/54

Power input of circulation pump

pressure loss [Pa]

flowrate [m3/s]

efficiency 15 %

power input: 24 (LF) 140 W (HF)

annual consumption: Pe * 2000 h

46 kWh 280 kWh

VpPe

19/54

Safety and protection devices

pressures in system

safety valve

expansion vessel

20/54

Safety and protection devices

safety valve

protects the collector loop against non-permissible pressure

expansion vessel

allows changes of fluid volume (due to thermal expansion)

without extreme increase of pressure above non-perimissible

limit (safety valve will not react during standard operation)

21/54

Pressures in solar system

opening pressure of safety valve pSV

maximum operation pressure pe

kPa300f9,0

kPa300fkPa20

SVSVe

SVSVe

porpp

porpp

hydrostatic pressure ph

filling pressure p0

ds pghp 0

minimum operation pressure in highest

point pd = 20 kPa to ... kPa

operation pressure range

influences the sizing of expansion

vessel

22/54

Safety (relief) valve

relief pressure

respects pressure

endurance of system

components

influences size of

expansion vessel

cap

spring ring

membrane

screw joint

sealing

23/54

Safety (relief) valve

24/54

Boiling point

p0 pe

25/54

Location of safety valve

between safety valve and collector

must not be any valve

pressure loss at vapour mass flowrate

< 3 % of relief pressure

free outflow has to be assured from

relief

regular checks provided

no closurekg/h][

kWh/kg58.0

[kW]p

p

p

p

Q

r

Qm

26/54

Location of safety valve

27/54

Safety line

internal diameter of safety line

not less than 19 mm

maximum heat output of collector field for G = 1000 W/m2

SQd 4,115s

GAQ cS 0

28/54

Safety valve dimension

saddle cross section area

ps [kPa] 250 300 350 400 450 500 550 600 700 800 900 1000

K [kW.mm-2] 1,12 1,26 1,41 1,55 1,69 1,83 1,97 2,1 2,37 2,64 2,91 3,18

K

Q

W

SS

o [kW, mm2] for steam

saddle cross section area

SVW

SS

p

Q

2o [kW, kPa, mm2] for liquid

29/54

Safety valve dimension

DN 15 20 25 32 40

So 113 176 380 804 1017

w 0.444 0.565 0.684 0.693 0.549

30/54

Expansion vessel

closed solar systems

pressure expansion vessel with a membrane

31/54

Size of expansion vessel

minimum volume of expansion vessel

min. volume of fluid in EV in cold state Vs

1 – 10 % collector loop volume , min. 2 liters

change of fluid volume V in collector loop by thermal expansion bfrom t0 = 10 °C to tmax = 130 °C

absorbing collector volume Vc expelled at stagnation from

collectors (possibly to include piping above lowest part of collector)

cs VVVV bminEV,

32/54

Coefficient of thermal expansion

1)(

)(

)(

)()(

max

0

0

0max

t

t

tv

tvtv

b

33/54

Size of expansion vessel

pressure factor (usability of EV volume)

pe maximum pressure in solar system (relief pressure)

p0 minimum pressure in solar system (filling pressure)

pb atmospheric pressure (100 kPa)

be

e

pp

pp

0

0

EV100

pp

pVVVV

e

ecs

b (x 1.3)

34/54

Expansion vessel

selection of expansion vessel from a manufacturer predefined

sizes (closest higher volume)

35/54

Expansion vessel - location

right wrong

presetting pressure in EV: pv = p0 – 30 kPa

36/54

collectors 30 l

0.314 l/m x 100 m = 31 l

total collector loop volume 61 l

minimum volume in EV: 6 l

b * V = 0.1 * 50 l = 6 l

collector volume 30 l

VEV,min = 42 l

Expansion vessel sizing

37/54

relief pressure of pSV 600 kPa

max. pressure pe = 0.9 * 600 kPa = 540 kPa

hydrostatic ph = 15 * 1000 *9.81 = 150 kPa

minimum pressure p0 = ph + 30 kPa = 180 kPa

= (540-180)/640 = 0.56

VEN > 42 l * 1.3 / 0.56 = 98 l ... (140 l)

Expansion vessel sizing

38/54

Heat exchangers

power

temperature difference

efficiency

39/54

heat power transfer

from collector loop (collectors)

to secondary loops (storage, load)

liquid separation

collector loop (glycol)

secondary loop (heating water, hot water)

internal HX – inside stores (tube)

external HX – outside stores, separate (plate, tube)

Heat exchangers

40/54

Heat exchanger balance

//

1

/

1111 ttcMQ /

2

//

2222 ttcMQ

mtAUQQ 21solar

collectors

heat

exchangerheat

storage

41/54

heat power transferred = collector field heat power

first – select operation conditions, e.g.:

G = 1000 W/m2

te = 20 °C

tm = 40 – 50 °C

better several operation points – flowrate, temperature – very sensitive

Transferred heat power

2

210 emkemkk ttaAttaGAQ

42/54

Temperatures

mtAUQ

II

I

IIIm

lnt

t

ttt

maxmin

22

maxmin

11

max tC

tC

tC

tC

Q

Q

target > 75 %, tm < 8 K

thermal efficiency of HX

tmax

counterflow

43/54

defined operation point x dynamic behaviour in real operation

flowrates M1 a M2

given by hydraulic and pumps sizing

result of HX calculation (optimization)

heat power given by solar collector field Qk

temperatures at the input to HX are given by operation

primary (collector) loop

secondary loop

HX sizing = sizing U.A [W/K] – return calculation of temperature

conditions for selected size of HX

Boundary conditions

C6555/1 t

C2015/2 t

44/54

tube HX inside storage tank

U = 100 to 300 W/m2K A = 1 to 5 m2

(laminar flow, free convection)

Tube heat exchangers

45/54

swimming pool HX

U = 500 to 1000 W/m2K A = 0.2 to ... m2

(laminar / turbulent flow)

low pressure loss in pool circuit (large flowrates)

resistant to pool water (chlorides) – stainless steel

resistant to salty water – titan alloys

Shell and tube

46/54

plate counterflow HX outside the tank

U = 1000 to 3500 W/m2K A = 0.1 to 2 m2

(developed turbulent flow on both sides)

number and shape of plates defines the power output

soldered

screwed – demountable (cleaning)

Plate heat exchangers

47/54

Sizing with nomograms

0

40

800

50

100

150

200

250

300

350

400

450

500

0

10

30

50

70

90

450-500

400-450

350-400

300-350

250-300

200-250

150-200

100-150

50-100

0-50

m,1t m,2t

U A

48/54

Sizing with nomogramsco

rrec

tion

fact

or [%

]

corr

ectio

n fa

ctor

[%]

difference between input

temperatures [K]percentage of nominal flowrate [%]

49/54

Plate heat exchangers - software

50/54

Plate heat exchangers - software

51/54

low temperature difference from nominal 80/60 °C

lower flowrate, higher viscosity, laminar flowrate → lower heat transfer

coefficient

change of HX power

nominal power (80/60 °C – 20°C, 1,5 m3/h) = 150 kW

real power in solar system (55/45 °C – 20°C, 0,4 m3/h) = 5 kW

use of large HXs with higher area

lower output temperature to collectors – higher system efficiency

Change of heat power from nominal

mtAUQ

52/54

Change of operation conditions

50 °C

25 °C

47 °C

20 °C

Q = 20 kW

780 l/h 640 l/h

U = 1500 W/m2K

A = 4 m2

50 °C

33 °C

39 °C

20 °C

Q = 13.7 kW

780 l/h 640 l/h

U = 1900 W/m2K

A = 0.6 m2

93 % 63 %

tm = 3.3 K tm = 12 K

53/54

optimum temperature difference at HX with solar system with heat

power 240 kW (collector area 400 m2)

Optimization

Temperature difference [K] 10 8 6 4

Area [m2] 8,9 11,1 14,8 22,2

Increase of area [%] 100 125 166 250

System efficiency [%] 40,0 41,5 43,0 44,5

Paybakc time [years] 1,2 1,6 2,4

54/54

Operation

HX fouling

change of pressure loss

reduction of heat transfer, decrease

of power

heat insulation

temperature sensors at outputs

(function indication)