diff --git a/Cargo.lock b/Cargo.lock
index 76ce49c2..1083b9e7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1043,9 +1043,9 @@ dependencies = [
 
 [[package]]
 name = "ninterp"
-version = "0.2.0"
+version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e60a408704882574368061cb86dba333d64027a93d8634dfe39c85da167df2a5"
+checksum = "c6ad0d5c7daec14bf8d66d66eb1025ea4e24d0e2d6b0881fe3697d17054c88fe"
 dependencies = [
  "itertools 0.13.0",
  "ndarray 0.16.1",
diff --git a/cal_and_val/thermal/f3-vehicles/2020 Chevrolet Bolt EV.yaml b/cal_and_val/thermal/f3-vehicles/2020 Chevrolet Bolt EV.yaml
index d11c4d4d..716f8221 100644
--- a/cal_and_val/thermal/f3-vehicles/2020 Chevrolet Bolt EV.yaml	
+++ b/cal_and_val/thermal/f3-vehicles/2020 Chevrolet Bolt EV.yaml	
@@ -5,9 +5,9 @@ year: 2020
 cabin: 
   LumpedCabin:
     # 0.05 is Chad's uncalibrated estimate
-    cab_shell_htc_to_amb_watts_per_square_meter_degree_celsius: 0.05
+    cab_shell_htc_to_amb_watts_per_square_meter_kelvin: 0.05
     # 0.05 is Chad's uncalibrated estimate
-    cab_htc_to_amb_stop_watts_per_square_meter_degree_celsius: 0.05
+    cab_htc_to_amb_stop_watts_per_square_meter_kelvin: 0.05
     # 200,000 is Chad's uncalibrated estimate
     heat_capacitance_joules_per_kelvin: 200000
     # TODO: get actual vehicle length, but calibrate this later
diff --git a/cal_and_val/thermal/f3-vehicles/2021_Hyundai_Sonata_Hybrid_Blue.yaml b/cal_and_val/thermal/f3-vehicles/2021_Hyundai_Sonata_Hybrid_Blue.yaml
index 87543688..d4ab10cc 100644
--- a/cal_and_val/thermal/f3-vehicles/2021_Hyundai_Sonata_Hybrid_Blue.yaml
+++ b/cal_and_val/thermal/f3-vehicles/2021_Hyundai_Sonata_Hybrid_Blue.yaml
@@ -94,7 +94,7 @@ pt_type:
         FuelConverterThermal:
           heat_capacitance_joules_per_kelvin: 200000.0
           length_for_convection_meters: 1.0
-          htc_to_amb_stop_watts_per_square_meter_degree_celsius: 50.0
+          htc_to_amb_stop_watts_per_square_meter_kelvin: 50.0
           conductance_from_comb_watts_per_kelvin: 5.0
           max_frac_from_comb: 0.5
           tstat_te_sto_kelvin: 358.15
@@ -226,8 +226,8 @@ chassis:
   cargo_mass_kilograms: ~
 cabin:
   LumpedCabin:
-    cab_shell_htc_to_amb_watts_per_square_meter_degree_celsius: 0.05
-    cab_htc_to_amb_stop_watts_per_square_meter_degree_celsius: 0.05
+    cab_shell_htc_to_amb_watts_per_square_meter_kelvin: 0.05
+    cab_htc_to_amb_stop_watts_per_square_meter_kelvin: 0.05
     heat_capacitance_joules_per_kelvin: 200000.0
     length_meters: 2.5
     width_meters: 2.0
@@ -253,32 +253,3 @@ mass_kilograms: 1508.195
 pwr_aux_base_watts: 500.0
 trans_eff: 0.98
 save_interval: 1
-state:
-  i: 0
-  pwr_prop_fwd_max_watts: 0.0
-  pwr_prop_bwd_max_watts: 0.0
-  pwr_tractive_watts: 0.0
-  pwr_tractive_for_cyc_watts: 0.0
-  energy_tractive_joules: 0.0
-  pwr_aux_watts: 0.0
-  energy_aux_joules: 0.0
-  pwr_drag_watts: 0.0
-  energy_drag_joules: 0.0
-  pwr_accel_watts: 0.0
-  energy_accel_joules: 0.0
-  pwr_ascent_watts: 0.0
-  energy_ascent_joules: 0.0
-  pwr_rr_watts: 0.0
-  energy_rr_joules: 0.0
-  pwr_whl_inertia_watts: 0.0
-  energy_whl_inertia_joules: 0.0
-  pwr_brake_watts: 0.0
-  energy_brake_joules: 0.0
-  cyc_met: true
-  cyc_met_overall: true
-  speed_ach_meters_per_second: 0.0
-  dist_meters: 0.0
-  grade_curr: 0.0
-  elev_curr_meters: .nan
-  air_density_kilograms_per_cubic_meter: 1.172
-  mass_kilograms: .nan
diff --git a/fastsim-core/Cargo.toml b/fastsim-core/Cargo.toml
index bcb18e46..dfbce0b9 100644
--- a/fastsim-core/Cargo.toml
+++ b/fastsim-core/Cargo.toml
@@ -38,7 +38,7 @@ toml = { version = "0.8.12", optional = true }
 derive_more = { version = "1.0.0", features = ["from_str", "from", "is_variant", "try_into"] }
 ureq = { version = "2.9.1", optional = true }
 url = { version = "2.5.0", optional = true }
-ninterp = { version = "0.2.0", features = ["serde"] }
+ninterp = { version = "0.2.1", features = ["serde"] }
 
 [dev-dependencies]
 pretty_assertions = "1.4.1"
diff --git a/fastsim-core/fastsim-proc-macros/src/fastsim_api/fastsim_api_utils.rs b/fastsim-core/fastsim-proc-macros/src/fastsim_api/fastsim_api_utils.rs
index 5f696657..7e1c65da 100755
--- a/fastsim-core/fastsim-proc-macros/src/fastsim_api/fastsim_api_utils.rs
+++ b/fastsim-core/fastsim-proc-macros/src/fastsim_api/fastsim_api_utils.rs
@@ -193,8 +193,8 @@ pub(crate) fn impl_getters_and_setters(field: &mut syn::Field) -> Option<()> {
             "Ratio" => extract_units!(uom::si::ratio::ratio),
             "Time" => extract_units!(uom::si::time::second, uom::si::time::hour),
             "HeatTransferCoeff" => extract_units!(
-                uom::si::heat_transfer::watt_per_square_meter_degree_celsius,
-                uom::si::heat_transfer::watt_per_square_meter_kelvin
+                uom::si::heat_transfer::watt_per_square_meter_kelvin,
+                uom::si::heat_transfer::watt_per_square_meter_degree_celsius
             ),
             "HeatCapacity" => {
                 extract_units!(
@@ -202,7 +202,10 @@ pub(crate) fn impl_getters_and_setters(field: &mut syn::Field) -> Option<()> {
                     uom::si::heat_capacity::joule_per_degree_celsius
                 )
             }
-            "Temperature" => extract_units!(uom::si::temperature_interval::kelvin),
+            "TemperatureInterval" => extract_units!(uom::si::temperature_interval::kelvin),
+            "Temperature" => {
+                extract_units!(uom::si::thermodynamic_temperature::kelvin)
+            }
             "ThermalConductance" => {
                 extract_units!(uom::si::thermal_conductance::watt_per_kelvin)
             }
diff --git a/fastsim-core/src/gas_properties.rs b/fastsim-core/src/gas_properties.rs
index 7d663884..db65f09f 100644
--- a/fastsim-core/src/gas_properties.rs
+++ b/fastsim-core/src/gas_properties.rs
@@ -45,7 +45,7 @@ lazy_static! {
     #[pyo3(name = "get_therm_cond")]
     #[staticmethod]
     pub fn get_therm_cond_py(te_air: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_therm_cond(te_air * uc::KELVIN - *uc::CELSIUS_TO_KELVIN)?.get::<si::watt_per_meter_kelvin>())
+        Ok(Self::get_therm_cond((te_air + uc::CELSIUS_TO_KELVIN) * uc::KELVIN)?.get::<si::watt_per_meter_kelvin>())
     }
 
     /// Returns constant pressure specific heat [J/(kg*K)] of air
@@ -54,7 +54,7 @@ lazy_static! {
     #[pyo3(name = "get_specific_heat_cp")]
     #[staticmethod]
     pub fn get_specific_heat_cp_py(te_air: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_specific_heat_cp(te_air * uc::KELVIN - *uc::CELSIUS_TO_KELVIN)?.get::<si::joule_per_kilogram_kelvin>())
+        Ok(Self::get_specific_heat_cp((te_air + uc::CELSIUS_TO_KELVIN) * uc::KELVIN)?.get::<si::joule_per_kilogram_kelvin>())
     }
 
     /// Returns specific enthalpy [J/kg] of air  
@@ -63,7 +63,7 @@ lazy_static! {
     #[pyo3(name = "get_specific_enthalpy")]
     #[staticmethod]
     pub fn get_specific_enthalpy_py(te_air: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_specific_enthalpy(te_air * uc::KELVIN - *uc::CELSIUS_TO_KELVIN)?.get::<si::joule_per_kilogram>())
+        Ok(Self::get_specific_enthalpy((te_air  - uc::CELSIUS_TO_KELVIN) * uc::KELVIN)?.get::<si::joule_per_kilogram>())
     }
 
     /// Returns specific energy [J/kg] of air  
@@ -72,7 +72,7 @@ lazy_static! {
     #[pyo3(name = "get_specific_energy")]
     #[staticmethod]
     pub fn get_specific_energy_py(te_air: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_specific_energy(te_air * uc::KELVIN - *uc::CELSIUS_TO_KELVIN)?.get::<si::joule_per_kilogram>())
+        Ok(Self::get_specific_energy((te_air - uc::CELSIUS_TO_KELVIN) * uc::KELVIN)?.get::<si::joule_per_kilogram>())
     }
 
     /// Returns thermal Prandtl number of air
@@ -81,7 +81,7 @@ lazy_static! {
     #[pyo3(name = "get_pr")]
     #[staticmethod]
     pub fn get_pr_py(te_air: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_pr(te_air * uc::KELVIN - *uc::CELSIUS_TO_KELVIN)?.get::<si::ratio>())
+        Ok(Self::get_pr((te_air - uc::CELSIUS_TO_KELVIN) * uc::KELVIN )?.get::<si::ratio>())
     }
 
     /// Returns dynamic viscosity \[Pa*s\] of air
@@ -90,7 +90,7 @@ lazy_static! {
     #[pyo3(name = "get_dyn_visc")]
     #[staticmethod]
     pub fn get_dyn_visc_py(te_air: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_dyn_visc(te_air * uc::KELVIN - *uc::CELSIUS_TO_KELVIN)?.get::<si::pascal_second>())
+        Ok(Self::get_dyn_visc((te_air  - uc::CELSIUS_TO_KELVIN) * uc::KELVIN)?.get::<si::pascal_second>())
     }
 
     /// Returns temperature [°C] of air
@@ -99,7 +99,7 @@ lazy_static! {
     #[pyo3(name = "get_te_from_h")]
     #[staticmethod]
     pub fn get_te_from_h_py(h: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_te_from_h(h * uc::J_PER_KG)?.get::<si::kelvin>() - uc::CELSIUS_TO_KELVIN.value)
+        Ok(Self::get_te_from_h(h * uc::J_PER_KG)?.get::<si::degree_celsius>())
     }
 
     /// Returns temperature [°C] of air
@@ -108,7 +108,7 @@ lazy_static! {
     #[pyo3(name = "get_te_from_u")]
     #[staticmethod]
     pub fn get_te_from_u_py(u: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_te_from_u(u * uc::J_PER_KG)?.get::<si::kelvin>() - uc::CELSIUS_TO_KELVIN.value)
+        Ok(Self::get_te_from_u(u * uc::J_PER_KG)?.get::<si::degree_celsius>())
     }
 
 )]
@@ -151,7 +151,7 @@ impl Air {
     /// - `te_air`: temperature of air
     pub fn get_therm_cond(te_air: si::Temperature) -> anyhow::Result<si::ThermalConductivity> {
         Ok(
-            asp::THERMAL_CONDUCTIVITY_INTERP.interpolate(&[te_air.get::<si::kelvin>()])?
+            asp::THERMAL_CONDUCTIVITY_INTERP.interpolate(&[te_air.get::<si::degree_celsius>()])?
                 * uc::WATT_PER_METER_KELVIN,
         )
     }
@@ -162,35 +162,38 @@ impl Air {
     pub fn get_specific_heat_cp(
         te_air: si::Temperature,
     ) -> anyhow::Result<si::SpecificHeatCapacity> {
-        Ok(asp::C_P_INTERP.interpolate(&[te_air.get::<si::kelvin>()])? * uc::J_PER_KG_K)
+        Ok(asp::C_P_INTERP.interpolate(&[te_air.get::<si::degree_celsius>()])? * uc::J_PER_KG_K)
     }
 
     /// Returns specific enthalpy of air  
     /// # Arguments  
     /// - `te_air`: temperature of air
     pub fn get_specific_enthalpy(te_air: si::Temperature) -> anyhow::Result<si::SpecificEnergy> {
-        Ok(asp::ENTHALPY_INTERP.interpolate(&[te_air.get::<si::kelvin>()])? * uc::J_PER_KG)
+        Ok(asp::ENTHALPY_INTERP.interpolate(&[te_air.get::<si::degree_celsius>()])? * uc::J_PER_KG)
     }
 
     /// Returns specific energy of air  
     /// # Arguments  
     /// - `te_air`: temperature of air
     pub fn get_specific_energy(te_air: si::Temperature) -> anyhow::Result<si::SpecificEnergy> {
-        Ok(asp::ENERGY_INTERP.interpolate(&[te_air.get::<si::kelvin>()])? * uc::J_PER_KG)
+        Ok(asp::ENERGY_INTERP.interpolate(&[te_air.get::<si::degree_celsius>()])? * uc::J_PER_KG)
     }
 
     /// Returns thermal Prandtl number of air
     /// # Arguments
     /// - `te_air`: temperature of air     
     pub fn get_pr(te_air: si::Temperature) -> anyhow::Result<si::Ratio> {
-        Ok(asp::PRANDTL_INTERP.interpolate(&[te_air.get::<si::kelvin>()])? * uc::R)
+        Ok(asp::PRANDTL_INTERP.interpolate(&[te_air.get::<si::degree_celsius>()])? * uc::R)
     }
 
     /// Returns dynamic viscosity \[Pa*s\] of air
     /// # Arguments
     /// te_air: temperature of air
     pub fn get_dyn_visc(te_air: si::Temperature) -> anyhow::Result<si::DynamicViscosity> {
-        Ok(asp::DYN_VISC_INTERP.interpolate(&[te_air.get::<si::kelvin>()])? * uc::PASCAL_SECOND)
+        Ok(
+            asp::DYN_VISC_INTERP.interpolate(&[te_air.get::<si::degree_celsius>()])?
+                * uc::PASCAL_SECOND,
+        )
     }
 
     /// Returns temperature of air
@@ -247,7 +250,7 @@ mod air_static_props {
     use super::*;
     lazy_static! {
         /// Array of temperatures at which properties are evaluated
-        static ref TEMPERATURE_VALUES: Vec<si::Temperature> = [
+        static ref TEMPERATURE_DEG_C_VALUES: Vec<f64> = vec![
             -60.,
              -57.03690616,
             -53.1958198,
@@ -273,19 +276,16 @@ mod air_static_props {
             2947.10642291,
             3841.10336915,
             5000.
-        ]
-        .iter()
-        .map(|x| *x * uc::KELVIN + *uc::CELSIUS_TO_KELVIN)
-        .collect();
+        ];
         pub static ref TEMP_FROM_ENTHALPY: Interpolator = Interpolator::new_1d(
             ENTHALPY_VALUES.iter().map(|x| x.get::<si::joule_per_kilogram>()).collect::<Vec<f64>>(),
-            TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+            TEMPERATURE_DEG_C_VALUES.clone(),
             Strategy::Linear,
             Extrapolate::Error
         ).unwrap();
         pub static ref TEMP_FROM_ENERGY: Interpolator = Interpolator::new_1d(
             ENERGY_VALUES.iter().map(|x| x.get::<si::joule_per_kilogram>()).collect::<Vec<f64>>(),
-            TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+            TEMPERATURE_DEG_C_VALUES.clone(),
             Strategy::Linear,
             Extrapolate::Error
         ).unwrap();
@@ -321,7 +321,7 @@ mod air_static_props {
         .map(|x| *x * uc::WATT_PER_METER_KELVIN)
         .collect();
         pub static ref THERMAL_CONDUCTIVITY_INTERP: Interpolator = Interpolator::new_1d(
-            TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+            TEMPERATURE_DEG_C_VALUES.clone(),
             THERMAL_CONDUCTIVITY_VALUES.iter().map(|x| x.get::<si::watt_per_meter_degree_celsius>()).collect::<Vec<f64>>(),
             Strategy::Linear,
             Extrapolate::Error
@@ -358,7 +358,7 @@ mod air_static_props {
         .map(|x| *x * uc::J_PER_KG_K)
         .collect();
         pub static ref C_P_INTERP: Interpolator = Interpolator::new_1d(
-            TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+            TEMPERATURE_DEG_C_VALUES.clone(),
             C_P_VALUES.iter().map(|x| x.get::<si::joule_per_kilogram_kelvin>()).collect::<Vec<f64>>(),
             Strategy::Linear,
             Extrapolate::Error
@@ -394,7 +394,7 @@ mod air_static_props {
         .map(|x| *x * uc::J_PER_KG)
         .collect();
         pub static ref ENTHALPY_INTERP: Interpolator = Interpolator::new_1d(
-            TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+            TEMPERATURE_DEG_C_VALUES.clone(),
             ENTHALPY_VALUES.iter().map(|x| x.get::<si::joule_per_kilogram>()).collect::<Vec<f64>>(),
             Strategy::Linear,
             Extrapolate::Error
@@ -430,7 +430,7 @@ mod air_static_props {
         .map(|x| *x * uc::J_PER_KG)
         .collect();
         pub static ref ENERGY_INTERP: Interpolator = Interpolator::new_1d(
-            TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+            TEMPERATURE_DEG_C_VALUES.clone(),
             ENERGY_VALUES.iter().map(|x| x.get::<si::joule_per_kilogram>()).collect::<Vec<f64>>(),
             Strategy::Linear,
             Extrapolate::Error
@@ -466,7 +466,7 @@ mod air_static_props {
         .map(|x| *x * uc::PASCAL_SECOND)
         .collect();
         pub static ref DYN_VISC_INTERP: Interpolator = Interpolator::new_1d(
-            TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+            TEMPERATURE_DEG_C_VALUES.clone(),
             DYN_VISCOSITY_VALUES.iter().map(|x| x.get::<si::pascal_second>()).collect::<Vec<f64>>(),
             Strategy::Linear,
             Extrapolate::Error
@@ -478,7 +478,7 @@ mod air_static_props {
             .map(|((mu, c_p), k)| -> si::Ratio {*mu * *c_p / *k})
             .collect::<Vec<si::Ratio>>();
         pub static ref PRANDTL_INTERP: Interpolator = Interpolator::new_1d(
-            TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+            TEMPERATURE_DEG_C_VALUES.clone(),
             PRANDTL_VALUES.iter().map(|x| x.get::<si::ratio>()).collect::<Vec<f64>>(),
             Strategy::Linear,
             Extrapolate::Error
@@ -525,7 +525,7 @@ mod octane_static_props {
     use super::*;
     lazy_static! {
         /// Array of temperatures at which properties are evaluated
-        static ref TEMPERATURE_VALUES: Vec<si::Temperature> = [
+        static ref TEMPERATURE_DEG_C_VALUES: Vec<f64> = vec![
             -4.00000000e+01,
              -3.70369062e+01,
             -3.31958198e+01,
@@ -551,13 +551,10 @@ mod octane_static_props {
             2.96710642e+03,
             3.86110337e+03,
             5.02000000e+03
-        ]
-        .iter()
-        .map(|x| *x * uc::KELVIN + *uc::CELSIUS_TO_KELVIN)
-        .collect();
+        ];
         pub static ref TEMP_FROM_ENERGY: Interpolator = Interpolator::new_1d(
            ENERGY_VALUES.iter().map(|x| x.get::<si::joule_per_kilogram>()).collect::<Vec<f64>>(),
-           TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+           TEMPERATURE_DEG_C_VALUES.clone(),
            Strategy::Linear,
            Extrapolate::Error
         ).unwrap();
@@ -592,7 +589,7 @@ mod octane_static_props {
         .map(|x| *x * uc::J_PER_KG)
         .collect();
         pub static ref ENERGY_INTERP: Interpolator = Interpolator::new_1d(
-           TEMPERATURE_VALUES.iter().map(|x| x.get::<si::kelvin>()).collect::<Vec<f64>>(),
+           TEMPERATURE_DEG_C_VALUES.clone(),
            ENERGY_VALUES.iter().map(|x| x.get::<si::joule_per_kilogram>()).collect::<Vec<f64>>(),
            Strategy::Linear,
            Extrapolate::Error
@@ -607,7 +604,7 @@ mod octane_static_props {
     #[pyo3(name = "get_specific_energy")]
     #[staticmethod]
     pub fn get_specific_energy_py(te_octane: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_specific_energy(te_octane * uc::KELVIN - *uc::CELSIUS_TO_KELVIN)?.get::<si::joule_per_kilogram>())
+        Ok(Self::get_specific_energy((te_octane - uc::CELSIUS_TO_KELVIN) * uc::KELVIN )?.get::<si::joule_per_kilogram>())
     }
 
     /// Returns temperature [°C] of octane
@@ -616,7 +613,7 @@ mod octane_static_props {
     #[pyo3(name = "get_te_from_u")]
     #[staticmethod]
     pub fn get_te_from_u_py(u: f64) -> anyhow::Result<f64> {
-        Ok(Self::get_te_from_u(u * uc::J_PER_KG)?.get::<si::kelvin>() - uc::CELSIUS_TO_KELVIN.value)
+        Ok(Self::get_te_from_u(u * uc::J_PER_KG)?.get::<si::degree_celsius>())
     }
 )]
 #[derive(Deserialize, Serialize, Debug, Clone, PartialEq, HistoryMethods)]
@@ -629,7 +626,10 @@ impl Octane {
     /// # Arguments  
     /// - `te_octane`: temperature of octane
     pub fn get_specific_energy(te_octane: si::Temperature) -> anyhow::Result<si::SpecificEnergy> {
-        Ok(osp::ENERGY_INTERP.interpolate(&[te_octane.get::<si::kelvin>()])? * uc::J_PER_KG)
+        Ok(
+            osp::ENERGY_INTERP.interpolate(&[te_octane.get::<si::degree_celsius>()])?
+                * uc::J_PER_KG,
+        )
     }
 
     /// Returns temperature of octane
diff --git a/fastsim-core/src/si.rs b/fastsim-core/src/si.rs
index 50e7574d..f3ca284d 100644
--- a/fastsim-core/src/si.rs
+++ b/fastsim-core/src/si.rs
@@ -12,8 +12,8 @@ pub use si::f64::{
     Acceleration, Angle, Area, AvailableEnergy as SpecificEnergy, Curvature, DynamicViscosity,
     Energy, Force, Frequency, HeatCapacity, HeatTransfer as HeatTransferCoeff, InverseVelocity,
     Length, Mass, MassDensity, MomentOfInertia, Power, PowerRate, Pressure, Ratio,
-    SpecificHeatCapacity, SpecificPower, TemperatureInterval as Temperature, ThermalConductance,
-    ThermalConductivity, Time, Velocity, Volume,
+    SpecificHeatCapacity, SpecificPower, TemperatureInterval, ThermalConductance,
+    ThermalConductivity, ThermodynamicTemperature as Temperature, Time, Velocity, Volume,
 };
 pub use si::force::{newton, pound_force};
 pub use si::heat_capacity::{joule_per_degree_celsius, joule_per_kelvin};
@@ -33,6 +33,7 @@ pub use si::specific_power::{kilowatt_per_kilogram, watt_per_kilogram};
 pub use si::temperature_interval::kelvin;
 pub use si::thermal_conductance::watt_per_kelvin;
 pub use si::thermal_conductivity::{watt_per_meter_degree_celsius, watt_per_meter_kelvin};
+pub use si::thermodynamic_temperature::{degree_celsius, kelvin as kelvin_abs};
 pub use si::time::{hour, second};
 pub use si::velocity::{meter_per_second, mile_per_hour};
 pub use si::volume::cubic_meter;
diff --git a/fastsim-core/src/uc.rs b/fastsim-core/src/uc.rs
index e310cf72..3149b3e4 100644
--- a/fastsim-core/src/uc.rs
+++ b/fastsim-core/src/uc.rs
@@ -85,10 +85,8 @@ unit_const!(
     9.80
 );
 
-lazy_static::lazy_static! {
-    pub static ref CELSIUS_TO_KELVIN: crate::si::Temperature = 273.15 * KELVIN;
-}
 unit_const!(KELVIN, Temperature, 1.0);
+unit_const!(KELVIN_INT, TemperatureInterval, 1.0);
 unit_const!(J_PER_KG_K, SpecificHeatCapacity, 1.0);
 unit_const!(J_PER_K, HeatCapacity, 1.0);
 unit_const!(J_PER_KG, SpecificEnergy, 1.0);
@@ -96,3 +94,5 @@ unit_const!(PASCAL_SECOND, DynamicViscosity, 1.0);
 unit_const!(PASCAL, Pressure, 1.0);
 unit_const!(WATT_PER_METER_SQUARED_KELVIN, ThermalConductance, 1.0);
 unit_const!(WATT_PER_METER_KELVIN, ThermalConductivity, 1.0);
+
+pub const CELSIUS_TO_KELVIN: f64 = 273.15;
diff --git a/fastsim-core/src/vehicle/cabin.rs b/fastsim-core/src/vehicle/cabin.rs
index 934893c4..68b90742 100644
--- a/fastsim-core/src/vehicle/cabin.rs
+++ b/fastsim-core/src/vehicle/cabin.rs
@@ -108,7 +108,9 @@ impl LumpedCabin {
         self.state.pwr_thrml_to_res = pwr_thrml_to_res;
         // flat plate model for isothermal, mixed-flow from Incropera and deWitt, Fundamentals of Heat and Mass
         // Transfer, 7th Edition
-        let cab_te_film_ext = 0.5 * (self.state.temperature + te_amb_air);
+        let cab_te_film_ext: si::Temperature = 0.5
+            * (self.state.temperature.get::<si::kelvin_abs>() + te_amb_air.get::<si::kelvin_abs>())
+            * uc::KELVIN;
         self.state.reynolds_for_plate =
             Air::get_density(Some(cab_te_film_ext), Some(veh_state.elev_curr))
                 * veh_state.speed_ach
@@ -139,11 +141,17 @@ impl LumpedCabin {
                         * Air::get_therm_cond(cab_te_film_ext).with_context(|| format_dbg!())?
                         / self.length)
                     + 1.0 / self.cab_shell_htc_to_amb);
-            (self.length * self.width) * htc_overall_moving * (te_amb_air - self.state.temperature)
+            (self.length * self.width)
+                * htc_overall_moving
+                * (te_amb_air.get::<si::degree_celsius>()
+                    - self.state.temperature.get::<si::degree_celsius>())
+                * uc::KELVIN_INT
         } else {
             (self.length * self.width)
                 / (1.0 / self.cab_htc_to_amb_stop + 1.0 / self.cab_shell_htc_to_amb)
-                * (te_amb_air - self.state.temperature)
+                * (te_amb_air.get::<si::degree_celsius>()
+                    - self.state.temperature.get::<si::degree_celsius>())
+                * uc::KELVIN_INT
         };
 
         self.state.temp_prev = self.state.temperature;
diff --git a/fastsim-core/src/vehicle/hvac/hvac_sys_for_lumped_cabin.rs b/fastsim-core/src/vehicle/hvac/hvac_sys_for_lumped_cabin.rs
index 64ca339e..9e0ee146 100644
--- a/fastsim-core/src/vehicle/hvac/hvac_sys_for_lumped_cabin.rs
+++ b/fastsim-core/src/vehicle/hvac/hvac_sys_for_lumped_cabin.rs
@@ -14,7 +14,7 @@ pub struct HVACSystemForLumpedCabin {
     pub te_set: si::Temperature,
     /// deadband range.  any cabin temperature within this range of
     /// `te_set` results in no HVAC power draw
-    pub te_deadband: si::Temperature,
+    pub te_deadband: si::TemperatureInterval,
     /// HVAC proportional gain
     pub p: si::ThermalConductance,
     /// HVAC integral gain [W / K / s], resets at zero crossing events
@@ -47,7 +47,7 @@ impl Default for HVACSystemForLumpedCabin {
     fn default() -> Self {
         Self {
             te_set: *TE_STD_AIR,
-            te_deadband: 1.5 * uc::KELVIN,
+            te_deadband: 1.5 * uc::KELVIN_INT,
             p: Default::default(),
             i: Default::default(),
             d: Default::default(),
@@ -98,14 +98,22 @@ impl HVACSystemForLumpedCabin {
             (si::Power::ZERO, si::Power::ZERO, f64::NAN * uc::R)
         } else {
             // outside deadband
-            let te_delta_vs_set = cab_state.temperature - self.te_set;
-            let te_delta_vs_amb: si::Temperature = cab_state.temperature - te_amb_air;
+            let te_delta_vs_set = (cab_state.temperature.get::<si::degree_celsius>()
+                - self.te_set.get::<si::degree_celsius>())
+                * uc::KELVIN_INT;
+            let te_delta_vs_amb: si::TemperatureInterval =
+                (cab_state.temperature.get::<si::degree_celsius>()
+                    - te_amb_air.get::<si::degree_celsius>())
+                    * uc::KELVIN_INT;
 
             self.state.pwr_p = -self.p * te_delta_vs_set;
             self.state.pwr_i -= self.i * uc::W / uc::KELVIN / uc::S * te_delta_vs_set * dt;
             self.state.pwr_i = self.state.pwr_i.max(-self.pwr_i_max).min(self.pwr_i_max);
-            self.state.pwr_d =
-                -self.d * uc::J / uc::KELVIN * ((cab_state.temperature - cab_state.temp_prev) / dt);
+            self.state.pwr_d = -self.d * uc::J / uc::KELVIN
+                * ((cab_state.temperature.get::<si::degree_celsius>()
+                    - cab_state.temp_prev.get::<si::degree_celsius>())
+                    * uc::KELVIN_INT
+                    / dt);
 
             let (pwr_thrml_hvac_to_cabin, pwr_thrml_fc_to_cabin, cop) =
                 if cab_state.temperature > self.te_set + self.te_deadband {
@@ -116,7 +124,7 @@ impl HVACSystemForLumpedCabin {
                     // cop_ideal is t_c / (t_h - t_c) for cooling
 
                     // divide-by-zero protection and realistic limit on COP
-                    let cop_ideal = if te_delta_vs_amb.abs() < 5.0 * uc::KELVIN {
+                    let cop_ideal = if te_delta_vs_amb.abs() < 5.0 * uc::KELVIN_INT {
                         // cabin is cooler than ambient + threshold
                         // TODO: make this `5.0` not hardcoded
                         cab_state.temperature / (5.0 * uc::KELVIN)
@@ -181,7 +189,7 @@ impl HVACSystemForLumpedCabin {
     fn handle_heat_source(
         &mut self,
         te_fc: Option<si::Temperature>,
-        te_delta_vs_amb: si::Temperature,
+        te_delta_vs_amb: si::TemperatureInterval,
         pwr_thrml_hvac_to_cabin: &mut si::Power,
         cab_heat_cap: si::HeatCapacity,
         cab_state: LumpedCabinState,
@@ -199,7 +207,7 @@ impl HVACSystemForLumpedCabin {
                 *pwr_thrml_hvac_to_cabin = pwr_thrml_hvac_to_cabin
                     .min(
                         cab_heat_cap *
-                    (te_fc.unwrap() - cab_state.temperature)
+                    (te_fc.unwrap().get::<si::degree_celsius>() - cab_state.temperature.get::<si::degree_celsius>()) * uc::KELVIN_INT
                         * 0.1 // so that it's substantially less
                         / dt,
                     )
@@ -226,7 +234,7 @@ impl HVACSystemForLumpedCabin {
 
                 // divide-by-zero protection and realistic limit on COP
                 // TODO: make sure this is consist with above commented equation for heating!
-                let cop_ideal = if te_delta_vs_amb.abs() < 5.0 * uc::KELVIN {
+                let cop_ideal = if te_delta_vs_amb.abs() < 5.0 * uc::KELVIN_INT {
                     // cabin is cooler than ambient + threshold
                     // TODO: make this `5.0` not hardcoded
                     cab_state.temperature / (5.0 * uc::KELVIN)
diff --git a/fastsim-core/src/vehicle/hvac/hvac_sys_for_lumped_cabin_and_res.rs b/fastsim-core/src/vehicle/hvac/hvac_sys_for_lumped_cabin_and_res.rs
index c76a28e8..3058db19 100644
--- a/fastsim-core/src/vehicle/hvac/hvac_sys_for_lumped_cabin_and_res.rs
+++ b/fastsim-core/src/vehicle/hvac/hvac_sys_for_lumped_cabin_and_res.rs
@@ -14,7 +14,7 @@ pub struct HVACSystemForLumpedCabinAndRES {
     pub te_set: si::Temperature,
     /// Deadband range.  Any cabin temperature within this range of `te_set`
     /// results in no HVAC power draw
-    pub te_deadband: si::Temperature,
+    pub te_deadband: si::TemperatureInterval,
     /// HVAC proportional gain for cabin
     pub p_cabin: si::ThermalConductance,
     /// HVAC integral gain [W / K / s] for cabin, resets at zero crossing events  
@@ -62,7 +62,7 @@ impl Default for HVACSystemForLumpedCabinAndRES {
     fn default() -> Self {
         Self {
             te_set: *TE_STD_AIR,
-            te_deadband: 1.5 * uc::KELVIN,
+            te_deadband: 1.5 * uc::KELVIN_INT,
             p_cabin: Default::default(),
             i_cabin: Default::default(),
             d_cabin: Default::default(),
@@ -122,81 +122,108 @@ impl HVACSystemForLumpedCabinAndRES {
         let mut pwr_thrml_hvac_to_res: si::Power = self
             .solve_for_res(res_temp, res_temp_prev, dt)
             .with_context(|| format_dbg!())?;
-        let (cop_ideal, te_ref) =
-            if pwr_thrml_hvac_to_res + pwr_thrml_hvac_to_cabin > si::Power::ZERO {
-                // heating mode
-                // TODO: account for cabin and battery heat sources in COP calculation!!!!
+        let (cop_ideal, te_ref) = if pwr_thrml_hvac_to_res + pwr_thrml_hvac_to_cabin
+            > si::Power::ZERO
+        {
+            // heating mode
+            // TODO: account for cabin and battery heat sources in COP calculation!!!!
 
-                let (te_ref, te_delta_vs_amb) = if pwr_thrml_hvac_to_res > si::Power::ZERO {
-                    // both powers are positive -- i.e. both are in heating mode
+            let (te_ref, te_delta_vs_amb) = if pwr_thrml_hvac_to_res > si::Power::ZERO {
+                // both powers are positive -- i.e. both are in heating mode
 
-                    let te_ref: si::Temperature = if cab_state.temperature > res_temp {
-                        // cabin is hotter
-                        cab_state.temperature
-                    } else {
-                        // battery is hotter
-                        res_temp
-                    };
-                    (te_ref, te_ref - te_amb_air)
-                } else if pwr_thrml_hvac_to_res >= si::Power::ZERO {
-                    // `pwr_thrml_hvac_to_res` dominates need for heating
-                    (res_temp, res_temp - te_amb_air)
+                let te_ref: si::Temperature = if cab_state.temperature > res_temp {
+                    // cabin is hotter
+                    cab_state.temperature
                 } else {
-                    // `pwr_thrml_hvac_to_res` dominates need for heating
-                    (cab_state.temperature, cab_state.temperature - te_amb_air)
+                    // battery is hotter
+                    res_temp
                 };
+                (
+                    te_ref,
+                    (te_ref.get::<si::degree_celsius>() - te_amb_air.get::<si::degree_celsius>())
+                        * uc::KELVIN_INT,
+                )
+            } else if pwr_thrml_hvac_to_res >= si::Power::ZERO {
+                // `pwr_thrml_hvac_to_res` dominates need for heating
+                (
+                    res_temp,
+                    (res_temp.get::<si::degree_celsius>() - te_amb_air.get::<si::degree_celsius>())
+                        * uc::KELVIN_INT,
+                )
+            } else {
+                // `pwr_thrml_hvac_to_res` dominates need for heating
+                (
+                    cab_state.temperature,
+                    (cab_state.temperature.get::<si::degree_celsius>()
+                        - te_amb_air.get::<si::degree_celsius>())
+                        * uc::KELVIN_INT,
+                )
+            };
 
-                // https://en.wikipedia.org/wiki/Coefficient_of_performance#Theoretical_performance_limits
-                // cop_ideal is t_h / (t_h - t_c) for heating
-                // cop_ideal is t_c / (t_h - t_c) for cooling
+            // https://en.wikipedia.org/wiki/Coefficient_of_performance#Theoretical_performance_limits
+            // cop_ideal is t_h / (t_h - t_c) for heating
+            // cop_ideal is t_c / (t_h - t_c) for cooling
 
-                // divide-by-zero protection and realistic limit on COP
-                // TODO: make sure this is consistent with above commented equation for heating!
-                if te_delta_vs_amb.abs() < 5.0 * uc::KELVIN {
-                    // cabin is cooler than ambient + threshold
-                    // TODO: make this `5.0` not hardcoded
-                    (te_ref / (5.0 * uc::KELVIN), te_ref)
-                } else {
-                    (te_ref / te_delta_vs_amb.abs(), te_ref)
-                }
-            } else if pwr_thrml_hvac_to_res + pwr_thrml_hvac_to_cabin < si::Power::ZERO {
-                // cooling mode
-                // TODO: account for battery cooling source in COP calculation!!!!
+            // divide-by-zero protection and realistic limit on COP
+            // TODO: make sure this is consistent with above commented equation for heating!
+            if te_delta_vs_amb.abs() < 5.0 * uc::KELVIN_INT {
+                // cabin is cooler than ambient + threshold
+                // TODO: make this `5.0` not hardcoded
+                (te_ref / (5.0 * uc::KELVIN), te_ref)
+            } else {
+                (te_ref / te_delta_vs_amb.abs(), te_ref)
+            }
+        } else if pwr_thrml_hvac_to_res + pwr_thrml_hvac_to_cabin < si::Power::ZERO {
+            // cooling mode
+            // TODO: account for battery cooling source in COP calculation!!!!
 
-                let (te_ref, te_delta_vs_amb) = if pwr_thrml_hvac_to_res < si::Power::ZERO {
-                    // both powers are negative -- i.e. both are in cooling mode
+            let (te_ref, te_delta_vs_amb) = if pwr_thrml_hvac_to_res < si::Power::ZERO {
+                // both powers are negative -- i.e. both are in cooling mode
 
-                    let te_ref: si::Temperature = if cab_state.temperature < res_temp {
-                        // cabin is colder
-                        cab_state.temperature
-                    } else {
-                        // battery is colder
-                        res_temp
-                    };
-                    (te_ref, te_ref - te_amb_air)
-                } else if pwr_thrml_hvac_to_res >= si::Power::ZERO {
-                    // `pwr_thrml_hvac_to_cabin` dominates need for cooling
-                    (cab_state.temperature, cab_state.temperature - te_amb_air)
+                let te_ref: si::Temperature = if cab_state.temperature < res_temp {
+                    // cabin is colder
+                    cab_state.temperature
                 } else {
-                    // `pwr_thrml_hvac_to_res` dominates need for cooling
-                    (res_temp, res_temp - te_amb_air)
+                    // battery is colder
+                    res_temp
                 };
+                (
+                    te_ref,
+                    (te_ref.get::<si::degree_celsius>() - te_amb_air.get::<si::degree_celsius>())
+                        * uc::KELVIN_INT,
+                )
+            } else if pwr_thrml_hvac_to_res >= si::Power::ZERO {
+                // `pwr_thrml_hvac_to_cabin` dominates need for cooling
+                (
+                    cab_state.temperature,
+                    (cab_state.temperature.get::<si::kelvin_abs>()
+                        - te_amb_air.get::<si::degree_celsius>())
+                        * uc::KELVIN_INT,
+                )
+            } else {
+                // `pwr_thrml_hvac_to_res` dominates need for cooling
+                (
+                    res_temp,
+                    (res_temp.get::<si::degree_celsius>() - te_amb_air.get::<si::degree_celsius>())
+                        * uc::KELVIN_INT,
+                )
+            };
 
-                // https://en.wikipedia.org/wiki/Coefficient_of_performance#Theoretical_performance_limits
-                // cop_ideal is t_h / (t_h - t_c) for heating
-                // cop_ideal is t_c / (t_h - t_c) for cooling
+            // https://en.wikipedia.org/wiki/Coefficient_of_performance#Theoretical_performance_limits
+            // cop_ideal is t_h / (t_h - t_c) for heating
+            // cop_ideal is t_c / (t_h - t_c) for cooling
 
-                // divide-by-zero protection and realistic limit on COP
-                if te_delta_vs_amb.abs() < 5.0 * uc::KELVIN {
-                    // cooling-dominating component is cooler than ambient + threshold
-                    // TODO: make this `5.0` not hardcoded
-                    (te_ref / (5.0 * uc::KELVIN), te_ref)
-                } else {
-                    (te_ref / te_delta_vs_amb.abs(), te_ref)
-                }
+            // divide-by-zero protection and realistic limit on COP
+            if te_delta_vs_amb.abs() < 5.0 * uc::KELVIN_INT {
+                // cooling-dominating component is cooler than ambient + threshold
+                // TODO: make this `5.0` not hardcoded
+                (te_ref / (5.0 * uc::KELVIN), te_ref)
             } else {
-                (si::Ratio::ZERO, f64::NAN * uc::KELVIN)
-            };
+                (te_ref / te_delta_vs_amb.abs(), te_ref)
+            }
+        } else {
+            (si::Ratio::ZERO, f64::NAN * uc::KELVIN)
+        };
         self.state.cop = cop_ideal * self.frac_of_ideal_cop;
         ensure!(
             self.state.cop >= 0.0 * uc::R,
@@ -272,8 +299,8 @@ impl HVACSystemForLumpedCabinAndRES {
         cab_heat_cap: si::HeatCapacity,
         dt: si::Time,
     ) -> anyhow::Result<si::Power> {
-        let pwr_thrml_hvac_to_cabin = if cab_state.temperature <= self.te_set + self.te_deadband
-            && cab_state.temperature >= self.te_set - self.te_deadband
+        let pwr_thrml_hvac_to_cabin = if cab_state.temperature <= (self.te_set + self.te_deadband)
+            && cab_state.temperature >= (self.te_set - self.te_deadband)
         {
             // inside deadband; no hvac power is needed
 
@@ -283,7 +310,9 @@ impl HVACSystemForLumpedCabinAndRES {
             si::Power::ZERO
         } else {
             // outside deadband
-            let te_delta_vs_set = cab_state.temperature - self.te_set;
+            let te_delta_vs_set = (cab_state.temperature.get::<si::degree_celsius>()
+                - self.te_set.get::<si::degree_celsius>())
+                * uc::KELVIN_INT;
 
             self.state.pwr_p = -self.p_cabin * te_delta_vs_set;
             self.state.pwr_i -= self.i_cabin * uc::W / uc::KELVIN / uc::S * te_delta_vs_set * dt;
@@ -293,7 +322,10 @@ impl HVACSystemForLumpedCabinAndRES {
                 .max(-self.pwr_i_max_cabin)
                 .min(self.pwr_i_max_cabin);
             self.state.pwr_d = -self.d_cabin * uc::J / uc::KELVIN
-                * ((cab_state.temperature - cab_state.temp_prev) / dt);
+                * ((cab_state.temperature.get::<si::degree_celsius>()
+                    - cab_state.temp_prev.get::<si::degree_celsius>())
+                    * uc::KELVIN_INT
+                    / dt);
 
             let pwr_thrml_hvac_to_cabin: si::Power =
                 if cab_state.temperature > self.te_set + self.te_deadband {
@@ -361,7 +393,9 @@ impl HVACSystemForLumpedCabinAndRES {
             si::Power::ZERO
         } else {
             // outside deadband
-            let te_delta_vs_set = res_temp - self.te_set;
+            let te_delta_vs_set = (res_temp.get::<si::degree_celsius>()
+                - self.te_set.get::<si::degree_celsius>())
+                * uc::KELVIN_INT;
             self.state.pwr_p_res = -self.p_res * te_delta_vs_set;
             self.state.pwr_i_res -= self.i_res * uc::W / uc::KELVIN / uc::S * te_delta_vs_set * dt;
             self.state.pwr_i_res = self
@@ -369,8 +403,11 @@ impl HVACSystemForLumpedCabinAndRES {
                 .pwr_i_res
                 .max(-self.pwr_i_max_res)
                 .min(self.pwr_i_max_res);
-            self.state.pwr_d_res =
-                -self.d_res * uc::J / uc::KELVIN * ((res_temp - res_temp_prev) / dt);
+            self.state.pwr_d_res = -self.d_res * uc::J / uc::KELVIN
+                * ((res_temp.get::<si::degree_celsius>()
+                    - res_temp_prev.get::<si::degree_celsius>())
+                    * uc::KELVIN_INT
+                    / dt);
 
             let pwr_thrml_hvac_to_res: si::Power = if res_temp > self.te_set + self.te_deadband {
                 // COOLING MODE; Reversible Energy Storage is hotter than set point
@@ -429,7 +466,7 @@ impl HVACSystemForLumpedCabinAndRES {
                 *pwr_thrml_hvac_to_cabin = pwr_thrml_hvac_to_cabin
                     .min(
                         cab_heat_cap *
-                    (te_fc.unwrap() - cab_state.temperature)
+                    (te_fc.unwrap().get::<si::degree_celsius>() - cab_state.temperature.get::<si::degree_celsius>()) * uc::KELVIN_INT
                         * 0.1 // so that it's substantially less
                         / dt,
                     )
diff --git a/fastsim-core/src/vehicle/powertrain/fuel_converter.rs b/fastsim-core/src/vehicle/powertrain/fuel_converter.rs
index e731cc47..eb73be9b 100755
--- a/fastsim-core/src/vehicle/powertrain/fuel_converter.rs
+++ b/fastsim-core/src/vehicle/powertrain/fuel_converter.rs
@@ -514,7 +514,7 @@ pub struct FuelConverterThermal {
     /// parameter for temperature at which thermostat starts to open
     pub tstat_te_sto: Option<si::Temperature>,
     /// temperature delta over which thermostat is partially open
-    pub tstat_te_delta: Option<si::Temperature>,
+    pub tstat_te_delta: Option<si::TemperatureInterval>,
     #[serde(default = "tstat_interp_default")]
     pub tstat_interp: Interpolator,
     /// Radiator effectiveness -- ratio of active heat rejection from
@@ -553,7 +553,7 @@ lazy_static! {
     pub static ref GASOLINE_DENSITY: si::MassDensity = 0.75 * uc::KG / uc::L;
     /// TODO: find a source for this value
     pub static ref GASOLINE_LHV: si::SpecificEnergy = 33.7 * uc::KWH / uc::GALLON / *GASOLINE_DENSITY;
-    pub static ref TE_ADIABATIC_STD: si::Temperature= Air::get_te_from_u(
+    pub static ref TE_ADIABATIC_STD: si::Temperature = Air::get_te_from_u(
             Air::get_specific_energy(*TE_STD_AIR).with_context(|| format_dbg!()).unwrap()
                 + (Octane::get_specific_energy(*TE_STD_AIR).with_context(|| format_dbg!()).unwrap()
                     + *GASOLINE_LHV)
@@ -580,7 +580,9 @@ impl FuelConverterThermal {
     ) -> anyhow::Result<()> {
         self.state.pwr_thrml_fc_to_cab = pwr_thrml_fc_to_cab;
         // film temperature for external convection calculations
-        let te_air_film = 0.5 * (self.state.temperature + te_amb);
+        let te_air_film: si::Temperature = 0.5
+            * (self.state.temperature.get::<si::kelvin_abs>() + te_amb.get::<si::kelvin_abs>())
+            * uc::KELVIN;
         // Reynolds number = density * speed * diameter / dynamic viscosity
         // NOTE: might be good to pipe in elevation
         let fc_air_film_re =
@@ -588,40 +590,39 @@ impl FuelConverterThermal {
                 / Air::get_dyn_visc(te_air_film).with_context(|| format_dbg!())?;
 
         // calculate heat transfer coeff. from engine to ambient [W / (m ** 2 * K)]
-        self.state.htc_to_amb =
-            if veh_speed < 1.0 * uc::MPS {
-                // if stopped, scale based on thermostat opening and constant convection
-                self.state.tstat_open_frac =
-                    self.tstat_interp
-                        .interpolate(&[(self.state.temperature.get::<si::kelvin>()
-                            - uc::CELSIUS_TO_KELVIN.value)])
-                        .with_context(|| format_dbg!())?;
-                (uc::R + self.state.tstat_open_frac * self.radiator_effectiveness)
-                    * self.htc_to_amb_stop
-            } else {
-                // Calculate heat transfer coefficient for sphere,
-                // from Incropera's Intro to Heat Transfer, 5th Ed., eq. 7.44
-                let sphere_conv_params = get_sphere_conv_params(fc_air_film_re.get::<si::ratio>());
-                let htc_to_amb_sphere: si::HeatTransferCoeff = sphere_conv_params.0
-                    * fc_air_film_re.get::<si::ratio>().powf(sphere_conv_params.1)
-                    * Air::get_pr(te_air_film)
-                        .with_context(|| format_dbg!())?
-                        .get::<si::ratio>()
-                        .powf(1.0 / 3.0)
-                    * Air::get_therm_cond(te_air_film).with_context(|| format_dbg!())?
-                    / self.length_for_convection;
-                // if stopped, scale based on thermostat opening and constant convection
-                self.state.tstat_open_frac =
-                    self.tstat_interp
-                        .interpolate(&[(self.state.temperature.get::<si::kelvin>()
-                            - uc::CELSIUS_TO_KELVIN.value)])
-                        .with_context(|| format_dbg!())?;
-                self.state.tstat_open_frac * htc_to_amb_sphere
-            };
+        self.state.htc_to_amb = if veh_speed < 1.0 * uc::MPS {
+            // if stopped, scale based on thermostat opening and constant convection
+            self.state.tstat_open_frac = self
+                .tstat_interp
+                .interpolate(&[self.state.temperature.get::<si::degree_celsius>()])
+                .with_context(|| format_dbg!())?;
+            (uc::R + self.state.tstat_open_frac * self.radiator_effectiveness)
+                * self.htc_to_amb_stop
+        } else {
+            // Calculate heat transfer coefficient for sphere,
+            // from Incropera's Intro to Heat Transfer, 5th Ed., eq. 7.44
+            let sphere_conv_params = get_sphere_conv_params(fc_air_film_re.get::<si::ratio>());
+            let htc_to_amb_sphere: si::HeatTransferCoeff = sphere_conv_params.0
+                * fc_air_film_re.get::<si::ratio>().powf(sphere_conv_params.1)
+                * Air::get_pr(te_air_film)
+                    .with_context(|| format_dbg!())?
+                    .get::<si::ratio>()
+                    .powf(1.0 / 3.0)
+                * Air::get_therm_cond(te_air_film).with_context(|| format_dbg!())?
+                / self.length_for_convection;
+            // if stopped, scale based on thermostat opening and constant convection
+            self.state.tstat_open_frac = self
+                .tstat_interp
+                .interpolate(&[self.state.temperature.get::<si::degree_celsius>()])
+                .with_context(|| format_dbg!())?;
+            self.state.tstat_open_frac * htc_to_amb_sphere
+        };
 
         self.state.pwr_thrml_to_amb =
             self.state.htc_to_amb * PI * self.length_for_convection.powi(typenum::P2::new()) / 4.0
-                * (self.state.temperature - te_amb);
+                * (self.state.temperature.get::<si::degree_celsius>()
+                    - te_amb.get::<si::degree_celsius>())
+                * uc::KELVIN_INT;
 
         // let heat_to_amb = ;
         // assumes fuel/air mixture is entering combustion chamber at block temperature
@@ -638,14 +639,17 @@ impl FuelConverterThermal {
         // heat that will go both to the block and out the exhaust port
         self.state.pwr_fuel_as_heat = fc_state.pwr_fuel - (fc_state.pwr_prop + fc_state.pwr_aux);
         self.state.pwr_thrml_to_tm = (self.conductance_from_comb
-            * (self.state.te_adiabatic - self.state.temperature))
+            * (self.state.te_adiabatic.get::<si::degree_celsius>()
+                - self.state.temperature.get::<si::degree_celsius>())
+            * uc::KELVIN_INT)
             .min(self.max_frac_from_comb * self.state.pwr_fuel_as_heat);
-        let delta_temp: si::Temperature = ((self.state.pwr_thrml_to_tm
+        let delta_temp: si::TemperatureInterval = ((self.state.pwr_thrml_to_tm
             - self.state.pwr_thrml_fc_to_cab
             - self.state.pwr_thrml_to_amb)
             * dt)
             / self.heat_capacitance;
         self.state.temp_prev = self.state.temperature;
+        // Interestingly, it seems to be ok to add a `TemperatureInterval` to a `Temperature` here
         self.state.temperature += delta_temp;
 
         self.state.eff_coeff = match self.fc_eff_model {
@@ -690,19 +694,19 @@ impl Init for FuelConverterThermal {
     fn init(&mut self) -> anyhow::Result<()> {
         self.tstat_te_sto = self
             .tstat_te_sto
-            .or(Some(85. * uc::KELVIN + *uc::CELSIUS_TO_KELVIN));
-        self.tstat_te_delta = self.tstat_te_delta.or(Some(5. * uc::KELVIN));
+            .or(Some((85. + uc::CELSIUS_TO_KELVIN) * uc::KELVIN));
+        self.tstat_te_delta = self.tstat_te_delta.or(Some(5. * uc::KELVIN_INT));
         self.tstat_interp = Interpolator::new_1d(
             vec![
-                self.tstat_te_sto.unwrap().get::<si::kelvin>(),
-                self.tstat_te_sto.unwrap().get::<si::kelvin>()
+                self.tstat_te_sto.unwrap().get::<si::degree_celsius>(),
+                self.tstat_te_sto.unwrap().get::<si::degree_celsius>()
                     + self.tstat_te_delta.unwrap().get::<si::kelvin>(),
             ],
             vec![0.0, 1.0],
             Strategy::Linear,
             Extrapolate::Clamp,
         )
-        .with_context(|| format_dbg!())?;
+        .with_context(|| format_dbg!((self.tstat_te_sto, self.tstat_te_delta)))?;
         Ok(())
     }
 }
@@ -824,7 +828,7 @@ impl Default for FCTempEffModelLinear {
 #[derive(Debug, Clone, Deserialize, Serialize, PartialEq)]
 pub struct FCTempEffModelExponential {
     /// temperature at which `fc_eta_temp_coeff` begins to grow
-    pub offset: si::Temperature,
+    pub offset: si::TemperatureInterval,
     /// exponential lag parameter [K^-1]
     pub lag: f64,
     /// minimum value that `fc_eta_temp_coeff` can take
@@ -834,7 +838,7 @@ pub struct FCTempEffModelExponential {
 impl Default for FCTempEffModelExponential {
     fn default() -> Self {
         Self {
-            offset: 0.0 * uc::KELVIN + *uc::CELSIUS_TO_KELVIN,
+            offset: 0.0 * uc::KELVIN_INT,
             lag: 25.0,
             minimum: 0.2 * uc::R,
         }
diff --git a/fastsim-core/src/vehicle/powertrain/reversible_energy_storage.rs b/fastsim-core/src/vehicle/powertrain/reversible_energy_storage.rs
index 5973072c..47d0a004 100644
--- a/fastsim-core/src/vehicle/powertrain/reversible_energy_storage.rs
+++ b/fastsim-core/src/vehicle/powertrain/reversible_energy_storage.rs
@@ -218,8 +218,7 @@ impl ReversibleEnergyStorage {
                     / self.energy_capacity.get::<si::watt_hour>(),
                 te_res
                     .with_context(|| format_dbg!("Expected thermal model to be configured"))?
-                    .get::<si::kelvin>()
-                    - uc::CELSIUS_TO_KELVIN.value,
+                    .get::<si::degree_celsius>(),
             ],
             (Interpolator::Interp3D(..), RESEffInterpInputs::CRateSOCTemperature) => &[
                 state.pwr_out_electrical.get::<si::watt>()
@@ -227,8 +226,7 @@ impl ReversibleEnergyStorage {
                 state.soc.get::<si::ratio>(),
                 te_res
                     .with_context(|| format_dbg!("Expected thermal model to be configured"))?
-                    .get::<si::kelvin>()
-                    - uc::CELSIUS_TO_KELVIN.value,
+                    .get::<si::degree_celsius>(),
             ],
             _ => bail!(
                 "
@@ -855,10 +853,15 @@ impl RESLumpedThermal {
     ) -> anyhow::Result<()> {
         self.state.temp_prev = self.state.temperature;
         // TODO: make sure this impacts cabin temperature
-        self.state.pwr_thrml_from_cabin =
-            self.conductance_to_cab * (te_cab - self.state.temperature);
+        self.state.pwr_thrml_from_cabin = self.conductance_to_cab
+            * (te_cab.get::<si::degree_celsius>()
+                - self.state.temperature.get::<si::degree_celsius>())
+            * uc::KELVIN_INT;
         self.state.pwr_thrml_hvac_to_res = pwr_thrml_hvac_to_res;
-        self.state.pwr_thrml_from_amb = self.conductance_to_cab * (te_amb - self.state.temperature);
+        self.state.pwr_thrml_from_amb = self.conductance_to_cab
+            * (te_amb.get::<si::degree_celsius>()
+                - self.state.temperature.get::<si::degree_celsius>())
+            * uc::KELVIN_INT;
         self.state.pwr_thrml_loss =
             res_state.pwr_out_electrical.abs() * (1.0 * uc::R - res_state.eff);
         self.state.temperature += (self.state.pwr_thrml_hvac_to_res