fix: resolve CLI solver state dimension mismatch

Removed mathematical singularity in HeatExchanger models (q_hot - q_cold = 0 was redundant) causing them to incorrectly request 3 equations without internal variables. Fixed ScrewEconomizerCompressor internal_state_len to perfectly align with the solver dimensions.

crates/components/src/heat_exchanger/condenser.rs

@@ -101,6 +101,20 @@ impl Condenser {
         self.saturation_temp = temp;
     }
 
+    /// Overrides the effective UA value [W/K] at runtime.
+    ///
+    /// Sets the UA scale factor so that `UA_nominal × scale = ua_value`.
+    /// Used by `MchxCondenserCoil` to apply fan-speed and air-density corrections.
+    pub fn set_ua(&mut self, ua_value: f64) {
+        let ua_nominal = self.inner.ua_nominal();
+        let scale = if ua_nominal > 0.0 {
+            ua_value / ua_nominal
+        } else {
+            1.0
+        };
+        self.inner.set_ua_scale(scale.max(0.0));
+    }
+
     /// Validates that the outlet quality is <= 1 (fully condensed or subcooled).
     ///
     /// # Arguments
@@ -243,7 +257,7 @@ mod tests {
     fn test_condenser_creation() {
         let condenser = Condenser::new(10_000.0);
         assert_eq!(condenser.ua(), 10_000.0);
-        assert_eq!(condenser.n_equations(), 3);
+        assert_eq!(condenser.n_equations(), 2);
     }
 
     #[test]
@@ -305,7 +319,7 @@ mod tests {
         let condenser = Condenser::new(10_000.0);
 
         let state = vec![0.0; 10];
-        let mut residuals = vec![0.0; 3];
+        let mut residuals = vec![0.0; 2];
 
         let result = condenser.compute_residuals(&state, &mut residuals);
         assert!(result.is_ok());