diff --git a/data/energy_systems/heat_pumps/constants.yaml b/data/energy_systems/heat_pumps/constants.yaml
index 38d5f125..a9d98713 100644
--- a/data/energy_systems/heat_pumps/constants.yaml
+++ b/data/energy_systems/heat_pumps/constants.yaml
@@ -18,3 +18,11 @@ AuxHeaterEfficiency: 0.9
 ElecGridEF: 0.5
 ElectricityPrice: 0.073
 
+# Water to Water HP constants
+HPNominalCapacity: 256
+LowestPossibleLoadFlow: 4.73
+HighestPossibleLoadFlow: 9.46
+
+
+
+