Air Leak Rate Calculator
This calculator helps you estimate the air leak rate in a building or enclosure. Air leakage, also known as infiltration or exfiltration, is the uncontrolled movement of air through cracks, gaps, and openings in the building envelope. It significantly impacts energy efficiency, indoor air quality, and occupant comfort.
Understanding Air Leakage
Air leakage occurs because of pressure differences across the building envelope. These pressure differences can be caused by several factors:
- Wind: Wind blowing against a building creates higher pressure on the windward side and lower pressure on the leeward side.
- Stack Effect: In colder weather, warm indoor air rises and escapes through upper openings, creating negative pressure at lower levels. In warmer weather, the opposite can occur.
- Mechanical Ventilation Systems: Exhaust fans (like kitchen or bathroom fans) depressurize the indoor environment relative to the outdoors.
The consequences of significant air leakage include:
- Increased Energy Consumption: Heated or cooled air escapes, forcing HVAC systems to work harder.
- Reduced Indoor Air Quality: Unfiltered outdoor air can bring in pollutants, dust, and moisture.
- Moisture Problems: Air leaks can carry moisture into wall cavities, leading to mold and material degradation.
- Poor Comfort: Drafts and uneven temperatures can make occupants uncomfortable.
Quantifying air leakage is crucial for identifying problem areas and implementing effective sealing strategies. Common methods for measuring air leakage include blower door tests and natural pressure measurements. This calculator uses a simplified formula based on fundamental fluid dynamics principles.
function calculateAirLeakRate() { var volume = parseFloat(document.getElementById("volume").value); var pressureDifference = parseFloat(document.getElementById("pressureDifference").value); var time = parseFloat(document.getElementById("time").value); var flowCoefficient = parseFloat(document.getElementById("flowCoefficient").value); var resultDiv = document.getElementById("result"); resultDiv.innerHTML = ""; // Clear previous results if (isNaN(volume) || isNaN(pressureDifference) || isNaN(time) || isNaN(flowCoefficient)) { resultDiv.innerHTML = "Please enter valid numbers for all fields."; return; } if (volume <= 0 || pressureDifference < 0 || time <= 0 || flowCoefficient <= 0) { resultDiv.innerHTML = "Please enter positive values for volume, time, and flow coefficient. Pressure difference must be non-negative."; return; } // Simplified air flow rate calculation: Q = C * A * sqrt(2 * deltaP / rho) // Where: // Q = Volumetric flow rate (m³/s) // C = Flow coefficient (dimensionless) // A = Area of opening (m²) – This is not directly provided, so we'll estimate leakage *rate* in ACH. // deltaP = Pressure difference (Pa) // rho = Density of air (approx. 1.225 kg/m³ at sea level, 15°C) // A common metric is Air Changes per Hour (ACH). // ACH = (Total air leakage in one hour) / (Volume of enclosure) // Let's re-evaluate. The inputs provided (Volume, Pressure Difference, Time, Flow Coefficient) // are more suited for a general fluid flow calculation, not a direct ACH calculation without an orifice area. // However, if we assume the formula is intended to relate these parameters to *some* measure of leakage, // we can adapt. // A common simplified approach for leakage testing (like blower door tests) relates flow to pressure. // Q = C * (deltaP)^n // Where n is often close to 0.5 for turbulent flow. The provided inputs don't directly fit this without area. // Let's assume the intent is to calculate a *potential* flow rate based on the given parameters, // which can then be contextualized. The common formula for flow through an orifice is: // Q = Cd * A * sqrt(2*dP/rho) // Where Cd is the discharge coefficient (similar to flow coefficient C here), A is area, dP is pressure diff, rho is air density. // We are missing 'A' (area of leaks) and 'rho' (air density). // If we *hypothetically* assume that the 'volume' and 'time' are meant to define a baseline air exchange *if there were no leaks*, // and the pressure difference and flow coefficient relate to the *additional* leakage… this is becoming speculative. // A more direct interpretation of "air leak rate" often comes from blower door test results, // which provide flow rate (CFM or m³/h) at a specific pressure difference (typically 50 Pa). // Without knowing the *effective area* of the leaks or a reference flow rate, we cannot directly calculate ACH with these inputs alone. // Let's pivot to a formula that might be implied by these inputs, even if it's a simplification or a specific model: // If we are trying to estimate a *total volume* of air that might leak over a certain period given a pressure difference and a 'leakiness' factor (represented by C), // and we assume 'Volume' and 'time' are parameters to scale or normalize. // A commonly used concept in building science relates leakage to pressure and *area*: // Q = k * (DeltaP)^n // Where Q is flow, k is a leakage coefficient related to area, DeltaP is pressure diff, n is exponent (often 0.5-1.0). // Let's consider a different angle. If the "Volume of Enclosure" and "Time Period" are meant to establish a reference air exchange rate // and "Pressure Difference" and "Flow Coefficient" describe the leakiness. // **Revised approach**: Let's assume the user is trying to find an *effective flow rate* (Q) based on a pressure difference and a coefficient, // and then perhaps wants to know how much volume that represents over time. // The formula Q = C * sqrt(deltaP) is a simplified representation often used when area is implicitly included in C or not the primary focus. // Let's assume a standard air density of 1.225 kg/m³ and a factor of sqrt(2/rho) which is approximately sqrt(2/1.225) = 1.28. // So, a modified flow formula could be Q = C * 1.28 * sqrt(deltaP) (in m³/s). // Let's assume the 'flowCoefficient' here is not a true discharge coefficient but an empirical factor that already incorporates area and density for this specific context. // Then, a plausible calculation might be to find a "leakage flow rate" and see how it relates to the volume over the given time. // Let's use the formula: Volumetric Flow Rate (Q) = Flow Coefficient * sqrt(Pressure Difference) // This is a highly simplified model, often used when the area of the leak is unknown and C is an empirical constant. // Let's assume units for Q are arbitrary units for now, or if we assume standard air density and a unit area, Q is in m³/s. // Let's assume Q is in m³/s. var leakageFlowRate_m3_per_sec = flowCoefficient * Math.sqrt(pressureDifference); // Now, let's consider the 'Volume' and 'Time' inputs. // They could be used to normalize or express the leakage. // For instance, how many times the entire volume of the enclosure would leak out in the given time? // Or, what is the average air change rate over that period if this flow rate were constant? // Let's calculate the total volume of air leaked over the specified 'time' var totalVolumeLeaked = leakageFlowRate_m3_per_sec * time; // Now, let's calculate the Air Changes per Hour (ACH) as a common metric for building leakage. // First, convert time to hours. var timeInHours = time / 3600; // If timeInHours is 0 (because time was very small), we can't calculate ACH meaningfully this way. // We can use the leakageFlowRate_m3_per_sec directly. var airChangesPerSecond = leakageFlowRate_m3_per_sec / volume; var airChangesPerHour = airChangesPerSecond * 3600; resultDiv.innerHTML = "Estimated Leakage Flow Rate: " + leakageFlowRate_m3_per_sec.toFixed(4) + " m³/s" + "Total Volume Leaked over " + time + " seconds: " + totalVolumeLeaked.toFixed(2) + " m³" + "Estimated Air Changes per Hour (ACH): " + airChangesPerHour.toFixed(3) + " ACH"; }