HVAC Load Calculations - A Comprehensive Engineering Course

Building load calculations form the foundation of HVAC system design. The primary purpose of these calculations is to determine the maximum (peak) heating and cooling capacity required to maintain comfortable indoor conditions during the most extreme outdoor weather conditions. Unlike energy simulations that analyze annual performance, load calculations focus on "design day" conditions - the worst-case scenarios your system must handle.

A building's thermal load consists of three primary categories: envelope loads (heat transfer through walls, roofs, floors, and fenestration), internal loads (heat generated by people, lighting, and equipment inside the building), and ventilation loads (the energy required to condition outdoor air brought in for occupants). For cooling, all three components typically add heat to the space. For heating, envelope loads represent heat loss, while internal gains actually reduce the heating requirement.

The distinction between sensible and latent loads is critical for proper HVAC sizing. Sensible loads cause a change in air temperature (measured in BTU/hr or watts), while latent loads involve moisture addition or removal without temperature change. Cooling coils must handle both sensible heat (lowering temperature) and latent heat (removing humidity through condensation). The sensible heat ratio (SHR) - the ratio of sensible load to total load - directly impacts equipment selection and coil design.

Peak loads occur at different times depending on building orientation and usage patterns. A west-facing zone may peak at 4-5 PM due to afternoon solar gains, while an interior conference room might peak during a fully-occupied meeting. Understanding load timing is essential for proper system zoning and control strategies. Block loads (the sum of all zone peaks) differ from coincident loads (the actual simultaneous load), and this distinction affects central plant sizing.

Modern load calculation methods include ASHRAE's Radiant Time Series (RTS) method, the Heat Balance (HB) method used by EnergyPlus, and the simplified Cooling Load Temperature Difference/Solar Cooling Load (CLTD/SCL) method. Each offers different levels of accuracy and computational complexity. This course primarily covers the CLTD/SCL method for its practical applicability while introducing concepts from more rigorous approaches.

Heat transfer in buildings occurs through three fundamental mechanisms: conduction, convection, and radiation. Understanding each mode is essential for accurate load calculations. Conduction is the transfer of heat through solid materials by molecular vibration. In buildings, this occurs through wall assemblies, roof structures, floor slabs, and window glazing. Fourier's Law governs conductive heat transfer: Q = k * A * (T1 - T2) / L, where k is thermal conductivity, A is area, and L is thickness.

Convection transfers heat between surfaces and fluids (air) through molecular motion. In buildings, convection occurs at both interior and exterior surfaces. The convective heat transfer coefficient (h) depends on air velocity, surface orientation, and whether the surface is warmer or cooler than the air. Interior still-air film coefficients typically range from 1.0-1.5 BTU/hr-ft2-F, while exterior coefficients with 15 mph wind reach 4-6 BTU/hr-ft2-F. These surface films add significant thermal resistance to building assemblies.

Radiation heat transfer occurs through electromagnetic waves and requires no medium. All objects emit thermal radiation based on their temperature (Stefan-Boltzmann Law: Q = epsilon * sigma * A * T^4). In buildings, radiation is significant in two contexts: longwave radiation exchange between surfaces at different temperatures, and shortwave solar radiation entering through windows or absorbed by exterior surfaces. Solar radiation is the dominant cooling load component for many buildings.

The thermal resistance (R-value) method simplifies calculations by treating different heat transfer modes additively. For a wall assembly: R_total = R_outside_air + R_materials + R_inside_air. The overall heat transfer coefficient U = 1/R_total. This approach allows complex assemblies with multiple layers to be analyzed simply. Note that R-values are additive for series resistances (layers), but parallel paths (such as thermal bridges through framing) require weighted-average calculations.

Thermal bridging occurs when highly conductive materials (steel studs, concrete slabs, window frames) create paths of lower resistance through insulated assemblies. A steel stud wall may have nominal R-19 insulation but an effective R-value of only R-9 due to the studs. ASHRAE Standard 90.1 provides assembly U-factors that account for typical framing, and detailed calculations use area-weighted parallel-path or zone methods for accuracy.

Design conditions are the outdoor and indoor temperatures used to calculate peak loads. Outdoor design conditions come from statistical analysis of historical weather data - they represent extreme conditions that are exceeded only a small percentage of hours annually. The selection of design conditions directly impacts equipment capacity and first cost, making proper selection crucial for economical design.

ASHRAE publishes climatic design conditions in the Fundamentals Handbook (Chapter 14) and the online ASHRAE Weather Data Viewer. For cooling design, the most common conditions are the 0.4% and 1% annual values. The 0.4% condition means outdoor temperature exceeds this value only 35 hours per year (0.4% of 8760 hours). The 1% value is exceeded 88 hours annually. Most commercial projects use 0.4% conditions; residential projects often use 1% values. Alongside dry-bulb temperature, you need the mean coincident wet-bulb (MCWB) temperature for humidity calculations.

For heating design, ASHRAE provides 99.6% and 99% conditions - temperatures exceeded 99.6% or 99% of annual hours. The 99.6% heating design temperature occurs only during the coldest 35 hours of the year. Unlike cooling, humidity is rarely a concern for heating loads in most climates. However, extremely dry winter air may require humidification, adding a latent load to the heating system. Solar radiation data, wind speeds, and ground temperatures are also available for comprehensive analysis.

Indoor design conditions define the target environment your HVAC system must maintain. ASHRAE Standard 55 establishes comfort criteria based on operative temperature, humidity, air speed, and metabolic rate. Typical commercial cooling setpoints are 74-78F with 50% RH maximum; heating setpoints are 68-72F. Industrial and process applications may have tighter requirements - data centers require 64-80F with strict humidity control, while cleanrooms may need +/- 0.5F tolerance.

ASHRAE Standard 90.1 and IECC define eight climate zones (1-8, from hot to subarctic) with moisture designations (A=humid, B=dry, C=marine). Climate zones determine prescriptive envelope requirements, HVAC efficiency minimums, and economizer requirements. Zone 1A (Miami) has minimal heating loads but stringent cooling efficiency requirements, while Zone 7 (Duluth) prioritizes heating performance and envelope insulation. Always verify local amendments - California's Title 24 uses its own 16 climate zones.

Opaque envelope heat transfer through walls and roofs represents a significant portion of both heating and cooling loads. For heating calculations, the process is straightforward steady-state analysis: Q = U * A * (T_inside - T_outside). However, cooling calculations must account for solar radiation absorbed by exterior surfaces and the thermal mass effects that delay and attenuate heat flow into the space.

The Cooling Load Temperature Difference (CLTD) method simplifies transient heat transfer analysis by replacing the actual outdoor temperature with an equivalent temperature difference that accounts for both air-to-air temperature difference and solar effects. Q_cooling = U * A * CLTD, where CLTD values are tabulated for various wall and roof constructions, orientations, and times. CLTD values vary hourly - a west wall might have CLTD of 12F at noon but 45F at 5 PM due to afternoon sun and thermal lag.

Wall construction significantly affects CLTD values. Heavy mass walls (concrete, masonry) delay heat transfer by 6-10 hours compared to lightweight frame walls (2-4 hour lag). This "thermal mass effect" means a massive west wall's peak load occurs after sunset, potentially benefiting from cooler outdoor air for ventilation. ASHRAE Fundamentals Chapter 18 provides CLTD tables for wall groups (A through G) ranging from lightweight curtainwall to 12" concrete, and roof groups based on mass, insulation placement, and suspended ceiling presence.

Assembly U-factors must account for all components: exterior film, cladding, sheathing, insulation, framing, interior finish, and interior film. ASHRAE 90.1 Appendix A provides default assembly U-factors for common constructions. For metal buildings, standing seam roofs with compressed insulation require careful analysis - the effective U-factor may be 2-3 times the nominal insulation R-value due to thermal shorting at purlins. Continuous insulation (ci) installed outboard of framing dramatically improves assembly performance.

Below-grade walls and slab-on-grade floors require special treatment. Earth-contact surfaces have relatively stable temperatures (55-65F depending on climate) but complex heat paths. The F-factor method uses perimeter heat loss coefficients: Q = F * P_perimeter * (T_inside - T_ground), where F-factors depend on slab insulation configuration. For basement walls, the ASHRAE depth-dependent U-factor method accounts for varying soil temperatures with depth.

Fenestration (windows, curtainwall, skylights) is typically the largest contributor to cooling loads and a significant factor in heating loads. Unlike opaque walls, windows transmit solar radiation directly into the space while also conducting heat based on indoor-outdoor temperature difference. These two heat transfer modes - conduction and solar - must be calculated separately then combined.

Conductive heat transfer through windows follows the standard equation: Q_conduction = U * A * (T_out - T_in) for cooling or (T_in - T_out) for heating. However, window U-factors vary significantly with frame type, glazing configuration, and gas fill. Single-pane aluminum frame windows may have U = 1.2 BTU/hr-ft2-F, while high-performance triple-pane fiberglass frames achieve U = 0.15. NFRC-rated U-factors (required by code) include frame effects; center-of-glass values are lower.

Solar heat gain is the more complex and typically dominant component of window cooling loads. The Solar Heat Gain Coefficient (SHGC) indicates the fraction of incident solar radiation admitted through the window (both transmitted and absorbed-then-reradiated inward). Clear double-pane glass has SHGC around 0.70, while spectrally-selective low-e coatings reduce SHGC to 0.25-0.40 while maintaining visible light transmission. Q_solar = SHGC * A * E_incident, where E is solar irradiance (BTU/hr-ft2).

Solar irradiance varies dramatically by orientation, time, and date. Peak solar on a horizontal surface (skylight) occurs at noon during summer, reaching 250-300 BTU/hr-ft2. Vertical east and west surfaces peak at 200+ BTU/hr-ft2 during morning and afternoon respectively. South surfaces have consistent moderate values (150-180 BTU/hr-ft2) year-round. North surfaces receive only diffuse and ground-reflected radiation (30-60 BTU/hr-ft2). ASHRAE provides Solar Cooling Load (SCL) factors that combine solar intensity with thermal mass delay effects.

External shading devices (overhangs, fins, screens) significantly reduce solar gains. The projection factor (PF) - the ratio of horizontal projection to window height - determines shading effectiveness. A PF of 0.5 on south-facing glass can reduce summer solar gains by 50-70% while admitting beneficial winter sun at lower sun angles. Interior shading (blinds, drapes) is less effective since solar energy is already inside the thermal envelope - it may reduce radiant gain but not total energy. Shading coefficients (SC) from ASHRAE quantify reduction relative to unshaded clear glass.

Internal heat gains from people, lighting, and equipment often dominate cooling loads in commercial and industrial buildings. Unlike envelope loads that can be heating or cooling depending on outdoor conditions, internal gains are always heat additions that increase cooling requirements while offsetting heating loads. Accurate internal gain estimation requires understanding both the heat release rates and the diversity/usage patterns.

Occupant heat gain depends on activity level and is split between sensible (radiant and convective) and latent (moisture) components. A seated office worker generates approximately 250 BTU/hr sensible and 200 BTU/hr latent heat. Light manufacturing work increases to 300 sensible / 400 latent. Heavy work (gymnasium) reaches 525 sensible / 925 latent BTU/hr per person. ASHRAE Fundamentals Chapter 18 provides detailed tables. Note that latent gains affect humidity control and dehumidification coil sizing, not just temperature.

Lighting power density (LPD) varies by space type and is regulated by ASHRAE 90.1 and IECC. Current values range from 0.5 W/ft2 for corridors to 1.4 W/ft2 for retail. Office space typically allows 0.82 W/ft2. The heat gain equation is Q = 3.41 * W * F_usage * F_special, where 3.41 converts watts to BTU/hr. F_usage accounts for actual hours of operation vs. 24/7, and F_special includes factors like plenum return (where ~30% of recessed fixture heat enters the return air rather than the space).

Equipment plug loads are often the most uncertain component of internal gains. ASHRAE 90.1 provides receptacle power allowances (typically 0.75-1.5 W/ft2 for offices), but actual usage varies widely. Computer workstations generate 50-150W each; servers are 200-500W; copy machines 300-1000W. Kitchen equipment, medical devices, and laboratory equipment require specific analysis. Many equipment types also add moisture - coffee makers, dishwashers, and sterilizers contribute latent loads.

Diversity factors account for the fact that not all lights, equipment, and people are present simultaneously at peak conditions. A 100-person conference room rarely reaches full occupancy; computers cycle between active and idle states; peripheral office areas have lower usage than core spaces. Typical diversity factors range from 0.5-0.9 depending on building type and specific conditions. The building's schedule of operation (8-5 office vs. 24/7 hospital) significantly affects when internal gains align with envelope loads to create peak conditions.

Ventilation air - outdoor air intentionally brought into the building for occupant health - represents a significant portion of HVAC loads because this air must be heated or cooled from outdoor to supply conditions. ASHRAE Standard 62.1 "Ventilation for Acceptable Indoor Air Quality" establishes minimum outdoor air rates that engineers must incorporate into load calculations. Failure to properly account for ventilation loads leads to undersized equipment and poor indoor air quality.

The Ventilation Rate Procedure (VRP) in ASHRAE 62.1-2022 calculates breathing zone outdoor airflow as: Vbz = Rp * Pz + Ra * Az, where Rp is the per-person rate (typically 5 CFM/person for offices), Pz is zone population, Ra is the per-area rate (0.06 CFM/ft2 for offices), and Az is zone floor area. This additive formula accounts for both occupant-generated contaminants and building emissions. For a 1000 ft2 office with 10 people: Vbz = (5 * 10) + (0.06 * 1000) = 110 CFM.

The zone outdoor airflow (Voz) accounts for air distribution effectiveness: Voz = Vbz / Ez, where Ez depends on supply air configuration. Ceiling supply with ceiling return (typical) has Ez = 1.0. Ceiling supply with floor return has Ez = 1.2 (more effective). Floor supply with ceiling return (displacement ventilation) achieves Ez = 1.2 for heating and cooling zones. Personal ventilation systems can reach Ez up to 2.0. Lower Ez values (0.8-0.9) apply when supply air is warmer than space temperature (heating mode with ceiling diffusers).

For multi-zone systems (VAV, single-duct serving multiple zones), system ventilation efficiency (Ev) accounts for the variation in outdoor air fraction across zones. The outdoor air intake (Vot) equals the uncorrected sum divided by Ev: Vot = D * sum(Voz) / Ev, where D is diversity (often 1.0). Calculating Ev requires the primary outdoor air fraction (Zp) for each zone and identification of the critical zone. This calculation becomes complex for large systems - software tools in J∆S Engineering Suite automate this process.

The sensible ventilation load equals Q_s = 1.08 * CFM * (T_outdoor - T_supply), where 1.08 = 60 min/hr * 0.075 lb/ft3 * 0.24 BTU/lb-F. The latent load is Q_l = 4840 * CFM * (W_outdoor - W_supply), where W is humidity ratio in lb/lb and 4840 = 60 * 0.075 * 1076 (latent heat of vaporization). At peak summer conditions (95F, 75F wb outdoor vs. 55F supply), ventilation can represent 30-50% of total cooling load. Energy recovery ventilators (ERVs) with 60-80% effectiveness can dramatically reduce ventilation loads.

Infiltration is uncontrolled outdoor air leakage into a building through cracks, gaps, and openings in the building envelope. Unlike ventilation (which is intentional and filtered), infiltration bypasses HVAC systems and enters directly into occupied spaces. Infiltration loads can be significant, particularly in older buildings with poor air sealing, and must be included in load calculations. Properly designed HVAC systems also maintain positive pressurization to minimize infiltration.

The crack method estimates infiltration based on measured or estimated leakage areas and pressure differentials across the envelope. Q = A * C * deltaP^n, where A is effective leakage area, C is a flow coefficient, deltaP is pressure difference (typically 4 Pa reference for component testing or actual building pressure), and n is a flow exponent (0.5-0.65). This method requires detailed knowledge of envelope construction quality but provides the most accurate estimates. Building commissioning often includes blower door testing to measure actual leakage rates.

The simpler air change method assumes infiltration based on building type and construction quality: Q_infiltration = (ACH * Volume) / 60, where ACH is air changes per hour. Tight commercial construction achieves 0.1-0.2 ACH, average construction 0.3-0.5 ACH, and leaky buildings 0.5-1.0+ ACH. Residential buildings typically range from 0.15 ACH (new code-compliant) to 1.0+ ACH (older homes). This method is useful for early design estimates but should be refined as envelope details are developed.

Stack effect drives infiltration in tall buildings due to indoor-outdoor temperature differences creating pressure differentials. Warm air rises, creating positive pressure at upper floors and negative pressure at lower floors during winter (reversed in summer). The neutral pressure plane (NPP) typically occurs at mid-height but shifts based on vertical compartmentalization. In a 20-story building with 70F indoor / 0F outdoor conditions, stack pressure can reach 0.5 inches water column - enough to make elevator doors difficult to open on lower floors.

Wind pressure on building surfaces creates both positive pressure on windward faces and negative pressure on leeward faces. P_wind = 0.00256 * Cp * V^2, where Cp is a pressure coefficient (-0.7 to +0.8 depending on location) and V is wind velocity in mph. Design wind speeds vary from 15-25 mph depending on climate. The combination of stack effect and wind creates complex pressure patterns that vary hourly and seasonally. Vestibules, revolving doors, and air curtains help control infiltration at frequently-used entrances.

A complete cooling load calculation combines envelope loads (walls, roofs, floors, windows), internal gains (people, lights, equipment), ventilation loads, and infiltration into a comprehensive zone-by-zone and system-level analysis. The calculation must be performed for multiple hours to identify the peak load time, as different load components peak at different times of day. Software automates this process, but understanding the underlying methodology enables engineers to validate results and troubleshoot issues.

Zone cooling loads should be calculated for each thermally distinct area served by a separate control device. The zone peak hour varies by orientation and internal load profile. A west-facing private office might peak at 4-5 PM when afternoon solar combines with occupant and equipment heat. An interior conference room peaks when fully occupied, regardless of time. The zone load equation is: Q_zone = Q_walls + Q_roof + Q_floor + Q_windows_cond + Q_windows_solar + Q_people + Q_lights + Q_equipment + Q_infiltration.

The CLTD/SCL/CLF method structures these calculations systematically. CLTD (Cooling Load Temperature Difference) applies to opaque surfaces. SCL (Solar Cooling Load) factors combine solar irradiance with thermal mass delay for windows. CLF (Cooling Load Factor) accounts for thermal storage effects from internal gains - not all heat generated becomes immediate cooling load. For example, a 100W lamp turned on at 8 AM generates increasing cooling load throughout the morning as room mass absorbs then releases heat.

System loads (for ductwork and AHU sizing) sum zone loads but must account for duct heat gain/loss (2-5% of load, depending on location), fan heat (2-4% added to supply air), and draw-through vs. blow-through coil arrangements. The ventilation load is added at the system level since outdoor air is mixed with return air at the AHU. Total system load = sum(zone loads) + duct gain + fan heat + ventilation load.

Plant loads (for chiller and boiler sizing) use coincident rather than block loads. If Zone A peaks at 2 PM with 50 tons and Zone B peaks at 5 PM with 40 tons, the block load is 90 tons, but the coincident load might be 75 tons (sum at any single hour). Diversity factors (0.7-0.9) estimate coincident loads from block sums. Central plant should also include piping losses (2-3%) and pump heat. Safety factors (discussed in Section 11) are applied at this stage to arrive at final equipment capacity requirements.

Heating load calculations are fundamentally simpler than cooling loads because they assume steady-state conditions without solar effects or thermal mass time delays. The design condition represents the coldest expected outdoor temperature, typically during nighttime or early morning when internal gains are minimal and solar radiation is absent. This conservative approach ensures adequate heating capacity during worst-case conditions.

The basic heating load equation for opaque surfaces is Q = U * A * (T_inside - T_outside). Unlike cooling calculations, no CLTD correction is needed - the actual design temperature difference is used directly. For a wall with U = 0.06 BTU/hr-ft2-F, area of 1000 ft2, and design conditions of 72F indoor / 0F outdoor: Q = 0.06 * 1000 * (72-0) = 4,320 BTU/hr. Windows, being better insulators at night (no solar), still represent significant heat loss due to their higher U-factors.

Internal heat gains are typically NOT credited against heating loads for design purposes. Although lights and equipment operate during occupied hours, the design condition assumes minimum internal gains to ensure the heating system can maintain temperature during unoccupied periods (nights, weekends). Some engineers apply partial credit (50% of lighting, 25% of equipment) for buildings with continuous operation, but this requires careful judgment about actual conditions.

Ventilation and infiltration represent major heating loads because outdoor air at design conditions must be heated significantly (potentially 70-80F temperature rise). Using our ventilation formula: Q = 1.08 * CFM * deltaT. For 1000 CFM of outdoor air heated from 0F to 72F: Q = 1.08 * 1000 * 72 = 77,760 BTU/hr. This single component can exceed all envelope losses combined in well-insulated buildings. Demand-controlled ventilation (DCV) reduces outdoor air during low occupancy, substantially cutting heating loads.

Pickup (warm-up) load accounts for the extra capacity needed to bring a building from setback temperature to occupied setpoint in a reasonable time. After weekend setback from 72F to 55F, the building mass must be reheated. The pickup load depends on building mass (heavier = more stored energy), setback depth, and available warm-up time. Rules of thumb add 10-25% to design heating capacity for pickup, though detailed analysis considers specific building characteristics. Some high-mass buildings cannot achieve deep setback without prohibitive warm-up loads.

Safety factors account for calculation uncertainties, construction variations, future changes, and provide capacity margin for extreme conditions beyond design. However, excessive safety factors lead to oversized equipment with poor part-load efficiency, higher first cost, short-cycling, and humidity control problems. Modern engineering practice favors modest safety factors (5-15%) with careful documentation of assumptions rather than blanket multipliers.

Cooling equipment selection considers both total capacity and sensible heat ratio (SHR). A space with high latent loads (commercial kitchen, natatorium) requires equipment with lower SHR (more dehumidification capacity). Standard DX equipment SHR is 0.70-0.75; high-SHR units for sensible-dominated loads reach 0.85-0.90. Oversized cooling equipment short-cycles (runs briefly then shuts off), failing to achieve steady-state dehumidification - the result is cool but clammy conditions.

Variable capacity equipment (variable speed compressors, VRF systems, modulating boilers) tolerates broader sizing ranges because they modulate down to match actual loads. A VRF system sized 20% above calculated peak can operate efficiently at part load. Fixed-capacity equipment (single-stage packaged units, constant-speed chillers) requires tighter sizing (5-10% margin) to avoid efficiency losses. Multi-stage equipment (two-stage compressor, multiple chillers) provides intermediate flexibility.

The load calculation summary should document all assumptions: design conditions used, occupancy assumptions, lighting and equipment power densities, ventilation rates, infiltration estimates, and safety factors applied. Include a load breakdown showing percentage contributions from each component - this helps identify dominant loads and optimization opportunities. For example, if solar through west-facing glass represents 40% of peak cooling, exterior shading or spectrally-selective glazing could significantly reduce equipment size.

Equipment selection involves matching calculated loads to manufacturer catalog data. Catalog ratings are typically at ARI standard conditions (95F outdoor, 80F entering air, 67F ewb for cooling; 47F outdoor for heat pump heating). Correction factors adjust capacity for actual design conditions. A 10-ton unit at standard conditions might deliver only 9.2 tons at 105F outdoor. Heating equipment capacity also varies - furnaces are essentially constant output, but heat pump capacity drops dramatically in cold weather (capacity at 17F may be 50% of nominal rating).

Professional load calculation reports serve multiple purposes: they document the engineering analysis for permit review, provide a reference for equipment selection and specifications, enable future engineers to understand design basis, and demonstrate code compliance. A well-organized report clearly presents inputs, methodology, results, and conclusions in a format accessible to both technical and non-technical reviewers.

Report organization should follow a logical structure: project information (location, building type, gross area), design conditions (outdoor and indoor), building envelope summary (wall/roof/window areas and U-factors), internal load assumptions (occupancy, LPD, EPD), ventilation requirements, zone-by-zone load summaries, system load summaries, equipment selections, and code compliance verification. Include a methodology statement referencing ASHRAE procedures or software used. Each section should be self-contained but cross-referenced to related sections.

Zone load summaries should present peak loads (BTU/hr or tons), peak time, and load breakdown by component. A typical format shows rows for each load component (roof, walls, windows-conduction, windows-solar, people, lights, equipment, infiltration, ventilation) with sensible and latent columns. Include the design supply airflow (CFM) calculated from sensible load and supply temperature. Highlight zones with unusual characteristics - high solar exposure, process equipment, 24/7 operation - that require special attention.

Building and system summaries aggregate zone loads to determine central equipment requirements. Show block loads (sum of individual peaks), coincident peak (simultaneous sum at any hour), and diversity factor applied. Include heating and cooling loads separately since they require different equipment. For multi-system buildings, organize by system (AHU-1 serves zones 1-10, etc.) showing both connected zone load and system design load including ventilation, duct losses, and safety factors.

Code compliance documentation requirements vary by jurisdiction. ASHRAE 90.1 requires envelope compliance demonstration (prescriptive U-factors or performance trade-offs) and equipment efficiency verification. California Title 24 requires CF1R forms for residential and NRCC forms for nonresidential with specific documentation of envelope, mechanical, and lighting systems. IECC jurisdictions may require REScheck or COMcheck compliance reports. Electronic submissions increasingly link load calculations directly to compliance documents, requiring consistent and traceable data throughout.