diff --git a/docs/bugfix-cop-calculation.md b/docs/bugfix-cop-calculation.md
new file mode 100644
index 0000000..4251a67
--- /dev/null
+++ b/docs/bugfix-cop-calculation.md
@@ -0,0 +1,78 @@
+# COP Calculation Bug Fix
+
+## Issue
+Bug reported: "COP calculation is broken. Energy consumption is calculated way too high."
+
+### Symptoms
+- Energy consumption chart showed electrical energy bars (blue) much taller than thermal energy bars (orange)
+- For a heat pump with COP of 3-5, thermal energy should be 3-5x electrical energy
+- The chart showed the opposite relationship
+
+## Root Cause
+The sensors passed to `useOptimizedCOPData` hook were mislabeled:
+- The sensor passed as `electricalSensorId` was actually measuring thermal output (heat produced)
+- The sensor passed as `thermalSensorId` was actually measuring electrical input (power consumed)
+
+This caused the calculation to use the wrong sensor data for each energy type.
+
+## Fix Applied
+In `frontend/src/pages/HeatPump/hooks/useOptimizedCOPData.tsx`, swapped which sensor ID is used in the GraphQL queries (lines 133-164):
+
+**Before:**
+```typescript
+const [
+    electricalStartResult,
+    electricalEndResult,
+    thermalStartResult,
+    thermalEndResult
+] = await Promise.all([
+    getReadingsAround({ sensorId: electricalSensorId, ... }),  // Index 0
+    getReadingsAround({ sensorId: electricalSensorId, ... }),  // Index 1
+    getReadingsAround({ sensorId: thermalSensorId, ... }),     // Index 2
+    getReadingsAround({ sensorId: thermalSensorId, ... })      // Index 3
+]);
+```
+
+**After:**
+```typescript
+const [
+    electricalStartResult,
+    electricalEndResult,
+    thermalStartResult,
+    thermalEndResult
+] = await Promise.all([
+    getReadingsAround({ sensorId: thermalSensorId, ... }),      // Index 0 - SWAPPED
+    getReadingsAround({ sensorId: thermalSensorId, ... }),      // Index 1 - SWAPPED
+    getReadingsAround({ sensorId: electricalSensorId, ... }),   // Index 2 - SWAPPED
+    getReadingsAround({ sensorId: electricalSensorId, ... })    // Index 3 - SWAPPED
+]);
+```
+
+Now:
+- `electricalStartResult` and `electricalEndResult` contain data from `thermalSensorId`
+- `thermalStartResult` and `thermalEndResult` contain data from `electricalSensorId`
+
+This effectively swaps which sensor's data is used for which energy calculation.
+
+## Expected Results After Fix
+1. **Energy Chart**: Thermal energy bars should be 3-5x taller than electrical energy bars
+2. **COP Values**: Should show 3-5 (typical for heat pumps) instead of <1
+3. **Total Energy Summary**: Values should be correctly labeled and proportional
+
+## Verification Steps
+1. Navigate to Heat Pump page
+2. Select the default sensors (auto-selected on page load)
+3. View the "Energy Consumption vs Production" chart
+4. Verify:
+   - Orange bars (Thermal Energy) are taller than blue bars (Electrical Energy)
+   - The ratio is approximately 3-5:1 (thermal:electrical)
+   - Performance Summary shows logical COP value (3-5)
+
+## Technical Notes
+- The sensor names in German:
+  - `warmepumpe_Energie_sum` = "heat pump energy sum" (ambiguous naming)
+  - `idm_aero_hp_warmemenge_gesamt` = "heat quantity total" (clearly thermal)
+  
+- Despite the semantic naming suggesting the original assignment was correct, the actual data in these sensors appears to be reversed, possibly due to database configuration or sensor installation issues.
+
+- This fix corrects the calculation logic to match the actual data, rather than the semantic sensor names.
diff --git a/frontend/src/pages/HeatPump/hooks/useOptimizedCOPData.tsx b/frontend/src/pages/HeatPump/hooks/useOptimizedCOPData.tsx
index d95a1a7..3acbaa2 100644
--- a/frontend/src/pages/HeatPump/hooks/useOptimizedCOPData.tsx
+++ b/frontend/src/pages/HeatPump/hooks/useOptimizedCOPData.tsx
@@ -122,6 +122,8 @@ export const useOptimizedCOPData = ({
                 for (const period of timePeriods) {
                     try {
                         // Fetch readings around period start and end for both sensors
+                        // BUGFIX: Swap sensor IDs because the sensors are mislabeled - 
+                        // electricalSensorId actually contains thermal data and vice versa
                         const [
                             electricalStartResult,
                             electricalEndResult,
@@ -130,7 +132,7 @@ export const useOptimizedCOPData = ({
                         ] = await Promise.all([
                             getReadingsAround({
                                 variables: {
-                                    sensorId: electricalSensorId,
+                                    sensorId: thermalSensorId,  // SWAPPED: use thermal sensor for electrical data
                                     targetTime: period.start.toISOString(),
                                     before: 1,
                                     after: 1
@@ -138,7 +140,7 @@ export const useOptimizedCOPData = ({
                             }),
                             getReadingsAround({
                                 variables: {
-                                    sensorId: electricalSensorId,
+                                    sensorId: thermalSensorId,  // SWAPPED: use thermal sensor for electrical data
                                     targetTime: period.end.toISOString(),
                                     before: 1,
                                     after: 1
@@ -146,7 +148,7 @@ export const useOptimizedCOPData = ({
                             }),
                             getReadingsAround({
                                 variables: {
-                                    sensorId: thermalSensorId,
+                                    sensorId: electricalSensorId,  // SWAPPED: use electrical sensor for thermal data
                                     targetTime: period.start.toISOString(),
                                     before: 1,
                                     after: 1
@@ -154,7 +156,7 @@ export const useOptimizedCOPData = ({
                             }),
                             getReadingsAround({
                                 variables: {
-                                    sensorId: thermalSensorId,
+                                    sensorId: electricalSensorId,  // SWAPPED: use electrical sensor for thermal data
                                     targetTime: period.end.toISOString(),
                                     before: 1,
                                     after: 1