1/59 Heat sources for heat pumps - users.fs.cvut.cz
Transcript of 1/59 Heat sources for heat pumps - users.fs.cvut.cz
![Page 1: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/1.jpg)
1/59
Heat sources for heat pumps
ground
water
air
![Page 2: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/2.jpg)
2/59
Natural and waste energy
energy from solar radiation = ambient energy
- solar radiation: 200 to 1000 W/m2
- air
- precipitation, surface water, well water
- ground
geothermal water in specific areas
waste energy
technology processes, laundry, washing, ventilation
![Page 3: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/3.jpg)
3/59
specific power
heat flow from ambient 10 to 40 W/m2 (in average)
heat flow from Earth core 0,04 to 0,06 W/m2
temperature
under 2-5 m stable conditions > 10 °C
geothermic temperature gradient 3 K/100 m
thermal conductivity
dry sand soil 1,1 W/m.K
wet granite 3,3 W/m.K
Ground energy
average 2 W/m.K
![Page 4: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/4.jpg)
4/59
Ground temperature
temperature
dept
h
![Page 5: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/5.jpg)
5/59
vertical bore heat exchangers
drilled dry ground boreholes
horizontal ground heat exchangers
subsurface HX
wells
extraction of ground water – different technology, different heat
pump application
Ground energy extraction
![Page 6: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/6.jpg)
6/59
Ground vertical boreholes
heat extraction by dry
boreholes under 200 m
usually under 100 m
not space demanding
1 or 2 pipe circuits in borehole
primary circuit temperatures:
from -4 °C to +4 °C
![Page 7: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/7.jpg)
7/59
design of length and number of boreholes
thermal properties of the ground
risk of undersizing – reveals after years
decrease of heat output and COP, insufficient borehole regeneration
ecology
disruption of water horizons
interconnection of deep horizons with high quality ground water with
shallow horizons with low quality
Knowledge of geology !
![Page 8: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/8.jpg)
8/59
Ground vertical - Thermal resistance of
ground
]m.K/W[ln2
1
v
z
z
zd
DR
diameter of influenced
field
Dz = 4 to 6 m
diameter of borehole
dv = 100 to 150 mm
HDPE DN25, DN32
thermal conductivity
z = 1,0 to 3,0 W/m.K
bore
stable
field
influenced
field
HP
thermal resistance
![Page 9: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/9.jpg)
9/59
Ground vertical - Specific heat flow
]W/m[12,
z
vzlz
R
ttq
Ground type specific heat flow
qz,l [W/m]
granite with water 100
conductive stone 80
standard solid stone, average 55
dry sands, low conductivity 30
borehole temperature
tv12 = around 0 °C (+4 to – 4°C)
ground temperature in stable field
tz = 12 °C (+3 K/100 m)
![Page 10: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/10.jpg)
10/59
Ground vertical - Specific heat flow
EN 15 450 (VDI 4650)
annual extracted energy should be between 100 and 150 kWh/m
![Page 11: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/11.jpg)
11/59
Ground vertical - Depth (length) of
borehole
final borehole depth given by drilling technology – similar technology
to water wells, not more than 100 m
more boreholes = division of flowrate = lower pressure losses
for nominal conditions determine the heat power and COP
]m[z
vv
q
Ql
COPQQ kv
11
qz considered according to
assumed operation time of HP
(1800, 2400 h)
![Page 12: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/12.jpg)
12/59
Alternative sizing
determination of annual heat delivered by HP QHP,del and COP
determination of annual extracted energy from borehole Qv
operation period DtHP: 1800 (space heating only), 2400 (space
heating and DHW)
determination of average extraction power (at evaporator)
COPQQ delv
11
HP
vv
tD design power for borehole
depth calculation
![Page 13: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/13.jpg)
13/59
Borehole construction
suitable piping: HD-PE, PE-RC (crack resistant), PN16 (100m)
minimum distance > 5 m to avoid the coupling of influenced
fields
better > 10 m: drilling is not completely vertical (deflection 2
m), distance larger than 10 % of borehole length
ground water flow: suitable location of boreholes to avoid
mutual cooling
borehole filling by bentonite (cement mixture)
can’t be filled by extracted soil ! = insulator
![Page 14: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/14.jpg)
14/59
Borehole construction
injection pipe – filling the borehole with bentonite
reduction – connection of circuits
distance bar – distance between pipes
support bar
U piece – bottom of borehole
anchor
![Page 15: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/15.jpg)
15/59
Example: ground source HP boreholes
house, heat load 10 kW (te,N = -12 °C, ti = 20 °C)
heat pump QHP = 10 kW, COP = 4,0 (at B0/W35)
heating season, monovalent operation
te,av = 4,3 °C, ti,av = 20 °C, 225 days of heating, correction factor 0,75
space heating demand QSH
hot water demand QHW = 3.5 MWh/a
= 19,9 MWh/a NeNi
avgeavgi
NSHtt
ttQQ
,,
,,24225
6
,
106,3365
CWHWdayHW
HW
ttcVQ
![Page 16: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/16.jpg)
16/59
Example: ground source HP boreholes
theoretical approach (power approach)
cooling power of the heat pump Qv = QHP (1 − 1/COP)
borehole
z = 2,5 W/mK, dv = 150 mm, Dz = 4 m, tz = 12 °C, tv1 = +2 °C, tv2 = -2 °C
thermal resistence of ground
specific heat power qz = (tz − tv12)/Rz
borehole length (depth)
v
z
z
zd
DR ln
2
1
= 0,22 mK/W
= 7.5 kW
= 54 W/m
lv = 140 m]m[z
vv
q
Ql
![Page 17: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/17.jpg)
17/59
Example: ground source HP boreholes
practical approach (demand approach): heating only 1800 h
heat extracted by heat pump Qex = QSH*(1 − 1/COP)
average cooling power of heat pump Qv = Qex / 1800 h
tables: average soil with 1,5 < z < 3,0
borehole length (depth)
= 14,9 MWh
= 8.3 kW
lv = 138 m
qz = 60 W/m (1800 h)
![Page 18: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/18.jpg)
18/59
Example: ground source HP boreholes
practical approach (demand approach): SH+HW 2400 h
heat extracted Qex = (QSH + QHW)*(1 − 1/COP)
average cooling power of heat pump Qv = Qex / 2400 h
tables: average soil with 1,5 < z < 3,0
borehole length (depth)
= 17,5 MWh
= 7.3 kW
lv = 146 m
qz = 50 W/m (2400 h)
![Page 19: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/19.jpg)
19/59
Horizontal ground heat exchangers
heat extraction from
subsurface layer (up to 2 m
depth)
possible influence of vegetation
space demanding excavation
large land need
HX temperatures around 0 °C
![Page 20: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/20.jpg)
20/59
Horizontal ground heat exchangers
depth min. 0,2 m under non freezing level
h = 0,6 to 2 m
pipe distance (spacing)
s = min. 0,8 m to 1,1 m
HDPE pipes 25 – 40 mm
thermal conductivity
z = 1,0 to 3,0 W/m.K
]m.K/W[2sinh2
ln2
1
s
h
d
sR
z
z
non freezing level
![Page 21: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/21.jpg)
21/59
Horizontal ground heat exchangers
Soil type specific heat flow
qz,l [W/m]
dry sands, non cohesive 10 – 15
dry solid soil 15 – 20
moist solid soil 20 – 25
soil saturated with ground water 25 – 30
soil with ground water flow 35 – 40
]W/m[12,
z
vzlz
R
ttq
temperature in pipes
tv12 = around 0 °C (+4 to – 4°C)
temperature of ground
tz = 10 °C
![Page 22: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/22.jpg)
22/59
Length and area of ground HX
]m[z
elk
z
vv
q
PQ
q
Ql
]m[ 2
,, Az
v
lz
v
q
Q
q
sQS
for a distance s = 1 m
qz,l becomes qz,A
Soil type specific heat flow
qz,A [W/m2]
dry sands, non cohesive 10 – 15
dry solid soil 15 – 20
moist solid soil 20 – 25
soil saturated with ground water 25 – 30
soil with ground water flow 35 – 40
![Page 23: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/23.jpg)
23/59
Specific heat flow EN 15 450 (VDI 4650)
annual extracted energy should be between 50 and 70 kWh/m2
for nominal conditions determine heat power and COP (at B0/W35)
]m[ 2
,Az
v
q
QS
COPQQ kv
11
qz,A is considered according to
assumed operation time of HP
(1800, 2400 h)
![Page 24: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/24.jpg)
24/59
Alternative sizing
determination of annual heat delivered by HP QHP,del and COP
determination of annual extracted energy from borehole Qv
operation period DtHP: 1800 (space heating only), 2400 (space
heating and DHW)
determination of average extraction power (at evaporator)
COPQQ delv
11
HP
vv
tD design power for ground HX
area calculation
![Page 25: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/25.jpg)
25/59
Construction of ground HX
length of cirucits should not exceed 100 m for DN25 ... or 400 m
for DN40 (pressure loss)
distribution of flowrate to number of circuits
circuit from one pipe, no junctions
surface above HX – permeable for rain (no concrete of asphalt
layers) for regeneration
mind the roots!
documentation of piping location
![Page 26: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/26.jpg)
26/59
Construction of ground HX
![Page 27: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/27.jpg)
27/59
Connection to house (borehole, HX)
brines (tF < -10°C): propylenglycol-water (30 / 70 %)
ethanol-water (40 / 60 %)
pipe with slope from distributor – deaeration
similar lengths of circuits – easy hydraulic balancing
passage into building in insulated protector
safety distance from building constructions (basements) –
pipes under freezing point
attention for crossing the water installation
piping inside building in insulation – condensation and freezing
![Page 28: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/28.jpg)
28/59
Borehole connection to house
![Page 29: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/29.jpg)
29/59
Ground HX connection to house
![Page 30: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/30.jpg)
30/59
Distributor
distributor located outside:
platic casing
concrete casing
![Page 31: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/31.jpg)
31/59
Ground water
chemical quality
quantity
stable water temperature =
average annual air
temperature
![Page 32: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/32.jpg)
32/59
Water
warm waste water: cooling processes
t = 20 to 25 °C
surface water: rivers, lakes
t = 0 to 18 °C, temperature infulenced by ambient climate
ground water: wells, boreholes
t = 7 to 10 °C, uniform temperature during the year
geothermal water: deep boreholes
t = 10 to 13 °C, temperature gradient 3 K/100 m
t > 25 °C, geotermal water
![Page 33: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/33.jpg)
33/59
Ground water
pumping well (max. 15 m
deep: pump power)
drain well (15 m from pumping well)
cooling by 3 to 4 K
for Qk = 10 kW ~ 1500 l/h (0,4 kg/s)
]kg/s[
21 vvv
vv
ttc
QM
water quantity (constant flowrate)
pumping test: 30 days, or more !
pumping
well
drain
well
![Page 34: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/34.jpg)
34/59
Pumping and drain well
drain well pumping
well
HP
![Page 35: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/35.jpg)
35/59
Water quality
chemical content
corrosion (stainless steel) – chlorides, oxygen
minerals (heat exchanger fouling)
fine particles - filters with automatic cleaning
![Page 36: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/36.jpg)
36/59
Example: water well sizing
heat pump QHP = 10 kW, COP = 4,0
cooling power of the heat pump Qv = QHP (1 − 1/COP)
tv1 = 10 °C, Dt = 4 K
water flowrate Mw = 0,45 kg/s
= 7.5 kW
= 27 l/min
![Page 37: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/37.jpg)
37/59
Ambient air
use of ambient heat
heat power dependent on
climate conditions
winter: COP < 3
summer: COP > 4
mostly bivalent operation
removal of condensate
noise (large flowrates)
![Page 38: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/38.jpg)
38/59
Ambient air
0
100
200
300
400
500
600
700
800
I II III IV V VI VII VIII IX X XI XII
Qp
[k
Wh
]
-5
0
5
10
15
20
t e [
°C]
t e
temperature of air is lowest
in the time of highest heat demand
![Page 39: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/39.jpg)
39/59
Ambient air – energy content, enthalpy
xttxtcltch Da 184010.5,21010 6
0
ca specific heat of dry air, v J/(kg.K);
t air temperature, v °C;
l0 latent heat of water (evaporation), v J/kg;
cD specific heat of water vapour, v J/(kg.K);
x specific humidity of air, v kg w/kg da.
21 vv
vv
hh
QV
![Page 40: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/40.jpg)
40/59
Construction
indoor units outdoor units
![Page 41: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/41.jpg)
41/59
Indoor units
![Page 42: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/42.jpg)
42/59
Outdoor units
![Page 43: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/43.jpg)
43/59
Condensate
condensation of water content in air at evaporator of heat pump
removal of condensate
drainage to ground (outdoor units)
connection to sewer system
(indoor units)
transfer pump
concrete sheet
gravel layer condensate
removal
![Page 44: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/44.jpg)
44/59
Frost
frosting at evaporator surface
reduction of heat transfer
decrease of evaporator pressure and temperature, power, COP
reduction of cross section, increase of pressure loss, increase of fan
power, operation restriction
defrosting
internal cycle (favourable): hot vapor, reverse cycle
outter heating: electric cables at evaporator
by air above +3 °C, HP is OFF, fan is ON
![Page 45: 1/59 Heat sources for heat pumps - users.fs.cvut.cz](https://reader031.fdocuments.us/reader031/viewer/2022021308/62084391a4abb728dd20ca8a/html5/thumbnails/45.jpg)
45/59
Noise protection
large flowrates at evaporator, big fan - source of noise
grass not refection surfaces
noise barriers
(walls, green fences)
protection by distance
antivibrating layers under HP
noise reducers for piping (water, air)