Water vapor sorption in salt hydrates is one of the most promising means for compact, low loss, and long-term storage of solar heat in the built environment. One of the most interesting salt hydrates for compact seasonal heat storage is magnesium sulfate heptahydrate (MgSO47H2O). This paper describes the characterization of MgSO47H2O to examine its suitability for application in a seasonal heat storage system for the built environment. Both charging (dehydration) and discharging (hydration) behaviors of the material were studied using thermogravimetric differential scanning calorimetry, X-ray diffraction, particle distribution measurements, and scanning electron microscope. The experimental results show that MgSO47H2O can be dehydrated at temperatures below 150°C, which can be reached by a medium temperature (vacuum tube) collector. Additionally, the material was able to store 2.2GJ/m3, almost nine times more energy than can be stored in water as sensible heat. On the other hand, the experimental results indicate that the release of the stored heat is more difficult. The amount of water taken up and the energy released by the material turned out to be strongly dependent on the water vapor pressure, temperature, and the total system pressure. The results of this study indicate that the application of MgSO47H2O at atmospheric pressure is problematic for a heat storage system where heat is released above 40°C using a water vapor pressure of 1.3 kPa. However, first experiments performed in a closed system at low pressure indicate that a small amount of heat can be released at 50°C and a water vapor pressure of 1.3 kPa. If a heat storage system has to operate at atmospheric pressure, then the application of MgSO47H2O for seasonal heat storage is possible for space heating operating at 25°C and a water vapor pressure of 2.1 kPa.

1.
Visscher
,
K.
,
Veldhuis
,
J. B. J.
,
Oonk
,
H. A. J.
,
van Ekeren
,
P. J.
, and
Blok
,
J. G.
, 2004, “
Compacte Chemische Seizoenopslag Van Zonnewarmte; Eindrapportage
,” ECN Report No. ECN-C-04-074.
2.
Zondag
,
H. A.
,
Kalbasenka
,
A.
,
van Essen
,
V. M.
,
Bleijendaal
,
L. P. J.
,
Schuitema
,
R.
,
van Helden
,
W. G. J.
, and
Krosse
,
L.
, 2008, “
First Studies in Reactor Concepts for Thermochemical Storage
,” ECN Report No. ECN-M-9-008.
3.
Brown
,
M. E.
, 2001,
Introduction to Thermal Analysis; Techniques and Application
,
2nd ed.
,
Kluwer
,
Dordrecht
, Chap. 3, p.
4
.
4.
JCPDS-ICDD
, 1997, PDF crystallographic database, JCPDS-ICDD Powder Diffraction File (PDF-2), International Centre for Diffraction Data, Newtown Square, PA.
5.
Seeger
,
M.
,
Walter
,
O.
,
Flick
,
W.
,
Bickelhaupt
,
F.
, and
Akkerman
,
O. S.
, 2007,
Ullmann’s Encyclopedia of Industrial Chemistry
,
7th ed.
,
John Wiley and Sons, Inc.
, electronic release.
6.
Wagman
,
D. D.
,
Evans
,
W. H.
,
Parker
,
V. B.
,
Schumm
,
R. H.
, and
Halow
,
I.
, 1982, “
The NBS Tables of Chemical Thermodynamic Properties: Selected Values for Inorganic and C1 and C2 Organic Substances in SI Units
,”
J. Phys. Chem. Ref. Data
0047-2689,
11
, pp.
1
400
.
7.
Emons
,
H. H.
,
Ziegenbalf
,
G.
,
Naumann
,
R.
, and
Paulik
,
F.
, 1990, “
Thermal Decomposition of the Magnesium Sulfate Hydrates Under Quasi-Isothermal and Quasi-Isobaric Conditions
,”
J. Therm. Anal.
0368-4466,
36
, pp.
1265
1279
.
8.
Ruiz-Agudo
,
E.
,
Martin-Ramos
,
J. D.
, and
Rodriguez-Navarro
,
C.
, 2007, “
Mechanism and Kinetics of Dehydration of Epsomite Crystals Formed in the Presence of Organic Additives
,”
J. Phys. Chem. B
1089-5647,
111
(
1
), pp.
41
52
.
9.
Chipera
,
S. J.
, and
Vaniman
,
D. T.
, 2007, “
Experimental Stability of Magnesium Sulfate Hydrates That May Be Present on Mars
,”
Geochim. Cosmochim. Acta
0016-7037,
71
, pp.
241
250
.
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