GROUND-SOURCE HEAT PUMP SYSTEMS Dept. of Architecture, Ferrara University Economic performance of ground source heat pump: does it pay off? Laura Gabrielli, Michele Bottarelli 5 6 7 8 9 10 -15 -10 -5 0 5 10 COP * Tsource, [°C] T user = 45°C Q source Q user L L Q COP user = source user user T T T COP - = * T out T in T source T user
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GROUND-SOURCE HEAT PUMP SYSTEMSDept. of Architecture, Ferrara University
Economic performance of ground source heat pump: does it pay off?Laura Gabrielli, Michele Bottarelli
5
6
7
8
9
10
-15 -10 -5 0 5 10
CO
P*Tsource, [°C]
Tuser = 45°C
Qsource Quser
L
L
QCOP user=
sourceuser
user
TT
TCOP
−=*
Tout
Tin
Tsource
Tuser
GROUND-SOURCE HEAT PUMP SYSTEMSDept. of Architecture, Ferrara University
Economic performance of ground source heat pump: does it pay off?Laura Gabrielli, Michele Bottarelli
GROUND-SOURCE HEAT PUMP SYSTEMSDept. of Architecture, Ferrara University
Economic performance of ground source heat pump: does it pay off?Laura Gabrielli, Michele Bottarelli
Jan. Feb. Mar. Apr. May Jun July Aug. Sept. Oct. Nov. Dec.Cooling
Free
2010 O O O
2011 X X X X X X X X X X X X
2012 � � � � � � � � � � � �
2013 w w
GROUND-SOURCE HEAT PUMP SYSTEMSDept. of Architecture, Ferrara University
Economic performance of ground source heat pump: does it pay off?Laura Gabrielli, Michele Bottarelli
ESI – 1st International Conference – Pernik, 9-10 June, 2011European University Polytechnical
Field monitoring of a HGHE flat panelBottarelli & Di Federico
The flat-panel shows high energy performance:− 45 W/m in cooling mode, with a thermal
average working difference of 10 K− 80 W/m in heating mode, with a thermal
average working difference of 15 K
Similar temperatures were naturally achieved after few time of inactivity.
So, the heat transfer over the soil surface deletes the thermal memory of the energy exploitation carried out by shallow GHXs.
Unlike with the vertical exchangers, its behaviour highlights that long-term subsurface thermal energy build-up or depletion wouldn’t be expecting by shallow GHXs.
GROUND-SOURCE HEAT PUMP SYSTEMSDept. of Architecture, Ferrara University
Economic performance of ground source heat pump: does it pay off?Laura Gabrielli, Michele Bottarelli
Does GSHP pay off ?
Energy requirements
in heating
Building & operating cost
vs.
Climate zones
Energy labels
EMREnergy Mix Ratio
GROUND-SOURCE HEAT PUMP SYSTEMSDept. of Architecture, Ferrara University
Economic performance of ground source heat pump: does it pay off?Laura Gabrielli, Michele Bottarelli
France
Germany
Italy
Netherlands
Spain
Sweden
UK
1
23
4
5
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
€ 0.20 € 0.40 € 0.60 € 0.80 € 1.00 € 1.20 € 1.40
EM
R -
Ene
rgy
Mix
Ra
tio
Gas price for households, 2009 [€/Nm3]
Data from Europe's Energy Portal,
www.energy.eu
� Only heating mode� No reduction� GHE cost : 1 €/W� Cut-off: 30 y
GROUND-SOURCE HEAT PUMP SYSTEMSDept. of Architecture, Ferrara University
Economic performance of ground source heat pump: does it pay off?Laura Gabrielli, Michele Bottarelli
For shallow GHEs, PCMs could represent a method:1. to restore the UTES benefit, according to the
seasonally regeneration2. to smooth the thermal wave produced by the HP
Two kinds of energy requirement: heating & coolingThen, two melting points.
Thus, two PCMs are needed.
A numerical model has been implemented to analyze the benefit occurring by their application
A 2D numerical approach was carried out to assess the behaviour of a flat-panel with/without PCMs
2D transversal section 10x15 mPCM layer 30x170 cmN° elements 23.000Min element size 0.16 cm2
Max element size 1600 cm2
Model domain
COMSOL’s module:Heat Transfer in Solids, advanced
( )Tt
Tc eqeqeq ∇⋅∇=
∂∂ λρ
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
270 275 280 285 290 295 300
H [1
], D
[1/K
]
T [K]
D_waterD_PCMH_waterH_PCM
H&D functions
( ) Sii
n
iiG
n
ii Hrr λλ ⋅−⋅+⋅
− ∑∑==
1111
( )∑∑==
⋅−⋅+⋅
−n
i
SiiiG
n
ii THrr
11
)(11 ρρ
SOLID
LIQUID
( ) ( )( )∑=
⋅+⋅⋅n
ii
SLi
Lii TDhcTHr
11
( )( ) ( )( )∑∑==
⋅+⋅−⋅+⋅
−n
ii
SLi
SiiiG
n
ii TDhcTHrcr
11
11
( )∑=
⋅⋅n
ii
Lii THr
1
ρ
( )∑=
⋅⋅n
i
Liii THr
1
λ
Two functions (H&D) control the phase change in the model
H(T) controls the phase change D(T) modulates the latent heat
The latent heat was introduced as Equivalent Specific Heat
• Time varying heat flux at the GHE wall
• Time varying heat flux at the soil surface
• Constant temperature at the bottom• All other boundaries as adiabatic
Boundary conditions
0.5 100.1
T=15°C
q=
0 W
/m2
qGHE(t)
q=
0 W
/m2
qG(t)
0.2
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
389 390 391 392 393 394 395 396
Heat flux, [W
/m2
]Tem
per
atur
e, [°C
]
Day of Year
Air temperatureSoil surface temperatureGHE heat fluxSoil surface heat flux