floatval($_POST[‘builtupArea’]),
‘bedrooms’ => intval($_POST[‘bedrooms’]),
‘bathrooms’ => $_POST[‘bathrooms’],
‘occupants’ => intval($_POST[‘occupants’]),
‘radiators’ => intval($_POST[‘radiators’]),
‘houseType’ => $_POST[‘houseType’],
‘groundFloor’ => $_POST[‘groundFloor’],
‘firstFloor’ => $_POST[‘firstFloor’],
‘attic’ => $_POST[‘attic’],
‘atticInsulation’ => $_POST[‘atticInsulation’],
‘walls’ => $_POST[‘walls’],
‘windows’ => $_POST[‘windows’],
‘numWindows’ => intval($_POST[‘numWindows’]),
‘doors’ => $_POST[‘doors’],
‘numDoors’ => intval($_POST[‘numDoors’]),
‘postcode’ => $_POST[‘postcode’],
‘city’ => $_POST[‘city’],
‘address’ => $_POST[‘address’],
‘name’ => $_POST[‘name’],
’email’ => $_POST[’email’],
‘phone’ => $_POST[‘phone’]
];

// U-value mappings (W/m²K)
$uValues = [
‘walls’ => [
‘cavity’ => 0.3,
‘solid-brick’ => 2.1,
‘timber-frame’ => 0.22,
‘insulated-concrete’ => 0.18
],
‘windows’ => [
‘double-glazed’ => 2.8,
‘triple-glazed’ => 1.6,
‘upvc’ => 2.0,
‘aluminium’ => 2.2
],
‘doors’ => [
‘composite’ => 1.4,
‘upvc-door’ => 1.6,
‘wooden’ => 3.0,
‘steel’ => 1.2
],
‘atticInsulation’ => [
‘none’ => 2.0,
’10cm’ => 0.35,
’30cm’ => 0.13
]
];

// Heat loss multipliers based on house type
$houseTypeMultiplier = [
‘terraced’ => 0.85, // Less heat loss (shared walls)
‘end-terraced’ => 0.95, // Moderate heat loss
‘semi-detached’ => 1.0, // Standard
‘detached’ => 1.15, // More exposed
‘bungalow’ => 1.1 // More roof area
];

// Calculate heat loss
function calculateHeatLoss($data, $uValues, $houseTypeMultiplier) {
$area = $data[‘builtupArea’];

// Base calculation: Area-based heat loss
$baseHeatLoss = $area * 45; // Base: 45 W/m²

// Wall heat loss adjustment
$wallUValue = $uValues[‘walls’][$data[‘walls’]];
$wallArea = $area * 1.2; // Approximate wall area
$wallHeatLoss = $wallArea * $wallUValue * 21; // 21°C delta T

// Window heat loss
$windowUValue = $uValues[‘windows’][$data[‘windows’]];
$avgWindowArea = 1.5; // Average window size in m²
$totalWindowArea = $data[‘numWindows’] * $avgWindowArea;
$windowHeatLoss = $totalWindowArea * $windowUValue * 21;

// Door heat loss
$doorUValue = $uValues[‘doors’][$data[‘doors’]];
$avgDoorArea = 2.0; // Average door size in m²
$totalDoorArea = $data[‘numDoors’] * $avgDoorArea;
$doorHeatLoss = $totalDoorArea * $doorUValue * 21;

// Roof/Attic heat loss
$atticUValue = $uValues[‘atticInsulation’][$data[‘atticInsulation’]];
$roofArea = $area * 0.8; // Approximate roof area
$roofHeatLoss = $roofArea * $atticUValue * 21;

// Ventilation heat loss (based on occupants)
$ventilationHeatLoss = $data[‘occupants’] * 300; // 300W per person

// Total heat loss
$totalHeatLoss = $wallHeatLoss + $windowHeatLoss + $doorHeatLoss +
$roofHeatLoss + $ventilationHeatLoss;

// Apply house type multiplier
$totalHeatLoss *= $houseTypeMultiplier[$data[‘houseType’]];

// Add safety margin (15%)
$totalHeatLoss *= 1.15;

return round($totalHeatLoss / 1000, 1); // Convert to kW
}

// Calculate hot water demand
function calculateHotWater($occupants) {
// UK standard: 35-50 liters per person per day at 60°C
$dailyLiters = $occupants * 45;
$hotWaterLoad = ($dailyLiters * 4.186 * 35) / 3600; // kWh per day
return round($hotWaterLoad, 1);
}

// Recommend heat pump
function recommendHeatPump($heatLoad) {
$heatPumps = [
[‘model’ => ‘Daikin Altherma 3 H HT’, ‘capacity’ => 6, ‘price’ => 8500, ‘cop’ => 4.2],
[‘model’ => ‘Mitsubishi Ecodan 8kW’, ‘capacity’ => 8, ‘price’ => 9200, ‘cop’ => 4.3],
[‘model’ => ‘Vaillant aroTHERM plus 10kW’, ‘capacity’ => 10, ‘price’ => 10500, ‘cop’ => 4.5],
[‘model’ => ‘Samsung EHS Mono 12kW’, ‘capacity’ => 12, ‘price’ => 11800, ‘cop’ => 4.4],
[‘model’ => ‘LG Therma V R32 14kW’, ‘capacity’ => 14, ‘price’ => 13200, ‘cop’ => 4.6],
[‘model’ => ‘Panasonic Aquarea T-CAP 16kW’, ‘capacity’ => 16, ‘price’ => 14500, ‘cop’ => 4.5],
];

foreach ($heatPumps as $pump) {
if ($pump[‘capacity’] >= $heatLoad) {
return $pump;
}
}

// If none match, return the largest
return end($heatPumps);
}

// Calculate grant and costs
function calculateCosts($heatPump, $radiators, $numWindows, $numDoors) {
$equipmentCost = $heatPump[‘price’];
$installationCost = 3500; // Base installation

// Additional costs
$radiatorUpgrades = $radiators * 150; // £150 per radiator upgrade
$pipeworkCost = 1200;
$electricalCost = 800;

$totalCost = $equipmentCost + $installationCost + $radiatorUpgrades +
$pipeworkCost + $electricalCost;

// UK Boiler Upgrade Scheme (BUS) Grant
$busGrant = 7500; // £7,500 standard grant

$ownerPays = $totalCost – $busGrant;

return [
‘equipment’ => $equipmentCost,
‘installation’ => $installationCost,
‘radiators’ => $radiatorUpgrades,
‘pipework’ => $pipeworkCost,
‘electrical’ => $electricalCost,
‘total’ => $totalCost,
‘grant’ => $busGrant,
‘ownerPays’ => max(0, $ownerPays)
];
}

// Perform calculations
$heatLoad = calculateHeatLoss($data, $uValues, $houseTypeMultiplier);
$hotWaterLoad = calculateHotWater($data[‘occupants’]);
$totalLoad = $heatLoad + ($hotWaterLoad * 0.3); // Add 30% of hot water load

$recommendedPump = recommendHeatPump($totalLoad);
$costs = calculateCosts($recommendedPump, $data[‘radiators’], $data[‘numWindows’], $data[‘numDoors’]);

// Calculate annual savings
$gasCost = $totalLoad * 2000 * 0.10; // £0.10 per kWh gas
$heatPumpCost = ($totalLoad * 2000) / $recommendedPump[‘cop’] * 0.28; // £0.28 per kWh electricity
$annualSavings = max(0, $gasCost – $heatPumpCost);

?>

?>