diff --git a/VECTOAux/VectoAuxiliaries/Hvac/HVACConstants.vb b/VECTOAux/VectoAuxiliaries/Hvac/HVACConstants.vb
index dbe43d9244320fbcc9578f7b805116e8ea5977ed..51fb2270763d201c5f004ef8b4a9c37098c1258e 100644
--- a/VECTOAux/VectoAuxiliaries/Hvac/HVACConstants.vb
+++ b/VECTOAux/VectoAuxiliaries/Hvac/HVACConstants.vb
@@ -8,37 +8,43 @@
 '   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 '
 ' See the LICENSE.txt for the specific language governing permissions and limitations.
+Imports Newtonsoft.Json
 Imports TUGraz.VectoCommon.Utils
 
 Namespace Hvac
 	Public Class HVACConstants
 		Implements IHVACConstants
 
-		Private _fuelDensity As KilogramPerCubicMeter
+		<JsonProperty("FuelDensity")> ReadOnly _fuelDensity As Double
+		<JsonProperty("DieselGCVJperGram")> ReadOnly _dieselGcvJperGram As Double = 44800
 
 		Public Sub New()
-			_fuelDensity = 835.SI(Of KilogramPerCubicMeter)()
+			_fuelDensity = 835 '.SI(Of KilogramPerCubicMeter)()
 		End Sub
 
 		Public Sub New(fuelDensitySingle As KilogramPerCubicMeter)
-			_fuelDensity = fuelDensitySingle
+			_fuelDensity = fuelDensitySingle.Value()
 		End Sub
 
+
+		<JsonIgnore>
 		Public ReadOnly Property DieselGCVJperGram As JoulePerKilogramm Implements IHVACConstants.DieselGCVJperGram
 			Get
-				Return 44800.SI().Joule.Per.Gramm.Cast(Of JoulePerKilogramm)()
+				Return _dieselGcvJperGram.SI().Joule.Per.Gramm.Cast(Of JoulePerKilogramm)()
 			End Get
 		End Property
 
+		<JsonIgnore()>
 		Public ReadOnly Property FuelDensity As KilogramPerCubicMeter Implements IHVACConstants.FuelDensity
 			Get
-				Return _fuelDensity
+				Return _fuelDensity.SI(Of KilogramPerCubicMeter)()
 			End Get
 		End Property
 
+		<JsonIgnore()>
 		Public ReadOnly Property FuelDensityAsGramPerLiter As Double Implements IHVACConstants.FuelDensityAsGramPerLiter
 			Get
-				Return _fuelDensity.Value() * 1000
+				Return _fuelDensity * 1000
 			End Get
 		End Property
 	End Class
diff --git a/VECTOAux/VectoAuxiliariesTests/UnitTests/SSMTOOLTests.vb b/VECTOAux/VectoAuxiliariesTests/UnitTests/SSMTOOLTests.vb
index 30dc6b4560deb72206a5d403cc5f3f1b9521e8db..568ab56168241e1d61e2458d3992c5e595cf835d 100644
--- a/VECTOAux/VectoAuxiliariesTests/UnitTests/SSMTOOLTests.vb
+++ b/VECTOAux/VectoAuxiliariesTests/UnitTests/SSMTOOLTests.vb
@@ -525,10 +525,12 @@ Namespace UnitTests
 		Public Sub SaveAndRetreiveTest()
 
 			Const filePath As String = "SSMTOOLTestSaveRetreive.json"
+			Dim success As Boolean
 
 			Dim target As SSMTOOL = New SSMTOOL(filePath, New HVACConstants(), False, True)
 
-			target.Save(filePath)
+			success = target.Save(filePath)
+			Assert.IsTrue(success)
 
 			'change something
 			target.GenInputs.BP_BusLength = 202.202
@@ -536,7 +538,8 @@ Namespace UnitTests
 			Assert.AreEqual(target.GenInputs.BP_BusLength, 202.202)
 
 			'Retreive
-			target.Load(filePath)
+			success = target.Load(filePath)
+			Assert.IsTrue(success)
 
 			Assert.AreEqual(target.GenInputs.BP_BusLength, 10.655)
 		End Sub