Cooling Load Calculation Procedure - HVAC

Table of Contents

Obtenir les caractéristiques du bâtiment

Matériaux de construction.
Propriétés des matériaux de construction : valeurs U, valeurs R, coefficients d'ombrage, coefficients de gain de chaleur solaire.
Taille.
Couleur.
Forme.
Emplacement.
Orientation, N, S, E, W, NE, SE, SW, NW, etc.
Ombrage externe/interne.
Type d'occupation et heure de la journée.

Sélectionnez les conditions météorologiques de conception extérieure

Voirhttps://hvac-eng.com/weather-design-conditions-for-selected-locations/

Température.
Direction et vitesse du vent.
Conditions de sélection des conditions météorologiques de conception extérieure :

Type de structure, lourde, moyenne ou légère.
La structure est-elle isolée ? Si la structure est chauffée ou refroidie, la structure doit être isolée selon le code.
La structure est-elle exposée aux vents violents ?
Charge d’infiltration ou de ventilation.
Quantité de verre.
Heure d’occupation du bâtiment.
Type d'occupation du bâtiment.
Durée de température intérieure réduite.
Quelle est la plage de température quotidienne, minimum/maximum ?
Existe-t-il des variations significatives par rapport aux données météorologiques ASHRAE ?
Quel type d’appareils de chauffage sera utilisé ?
Coût prévu du carburant.

Sélectionnez la température intérieure de conception à maintenir dans chaque espace.

Voirhttps://hvac-eng.com/indoor-design-conditions/

Estimez les températures dans des espaces non conditionnés.
Sélectionnez et/ou calculez les valeurs U pour les murs, le toit, les fenêtres, les portes, les cloisons, etc.
Déterminez la superficie des murs, fenêtres, sols, portes, cloisons, etc.
Calculez les gains de chaleur par conduction pour tous les murs, fenêtres, sols, portes, cloisons, lucarnes, etc.
Calculez les gains de chaleur solaire pour tous les murs, fenêtres, sols, portes, cloisons, lucarnes, etc.
Les gains de chaleur par infiltration sont généralement ignorés, sauf si la tolérance à la température et à l’humidité de l’espace est critique.
Calculez le gain de chaleur de ventilation requis.
Calculez les gains de chaleur internes des lumières, des personnes et des équipements.
Calculez la somme de tous les gains de chaleur indiqués aux éléments G, H, I, J et K plus tôt dans cette liste.
Incluez une période de refroidissement matinale pour les bâtiments à utilisation intermittente et une configuration nocturne.
Tenez compte de la capacité excédentaire du système CVC autorisée pour la récupération matinale.
Tenez compte des équipements et des matériaux qui seront introduits dans le bâtiment au-dessus de la température intérieure de conception.
Les calculs de charge de refroidissement doivent être effectués à l'aide de méthodes acceptées par l'industrie pour déterminer les exigences réelles en matière de charge de refroidissement.

FREQUENTLY ASKED QUESTIONS

What are the key building characteristics that affect cooling load calculation?

The key building characteristics that affect cooling load calculation include construction materials, material properties (U-values, R-values, shading coefficients, solar heat gain coefficients), size, color, shape, location, orientation, external and internal shading, and occupancy type and time of day. These factors influence the amount of heat gain and loss through the building envelope, which in turn affects the cooling load. For example, a building with large windows and south-facing orientation will have a higher cooling load due to increased solar heat gain.

How do I select outdoor design weather conditions for cooling load calculation?

Selecting outdoor design weather conditions involves considering factors such as temperature, wind direction and speed, and other conditions specific to the location. The type of structure (heavy, medium, or light), insulation, exposure to high winds, infiltration or ventilation load, amount of glass, time of building occupancy, type of building occupancy, and length of reduced indoor temperature also influence the selection of outdoor design weather conditions. For example, a building in a hot and humid climate will require a higher outdoor design temperature than one in a mild climate.

What is the significance of infiltration and ventilation load in cooling load calculation?

Infiltration and ventilation load refer to the heat gain and loss through air leakage and intentional ventilation in a building. These loads can significantly impact the cooling load, especially in buildings with high occupancy rates or those located in areas with high outdoor temperatures. Infiltration and ventilation load can be estimated using various methods, including the air change per hour (ACH) method or the infiltration credit method. Accurate estimation of these loads is crucial to ensure that the cooling system is sized correctly.

How do I determine the indoor design temperature for each space in a building?

Determining the indoor design temperature for each space in a building involves considering factors such as the type of occupancy, activity level, and desired comfort level. For example, a office space may require a lower indoor design temperature than a warehouse or storage area. The indoor design temperature should also take into account the outdoor design weather conditions and the building’s construction characteristics. A general rule of thumb is to maintain an indoor design temperature between 22°C to 25°C (72°F to 77°F) for most commercial and residential buildings.

What is the impact of shading coefficients on cooling load calculation?

Shading coefficients represent the amount of solar radiation that is blocked by external shading devices such as overhangs, louvers, or blinds. A lower shading coefficient indicates more effective shading, which reduces the cooling load. Shading coefficients can be estimated using various methods, including the ASHRAE Clear Sky Model or the Solar Heat Gain Coefficient (SHGC) method. Accurate estimation of shading coefficients is crucial to ensure that the cooling system is sized correctly and to optimize energy efficiency.

Can you explain the concept of solar heat gain coefficients in cooling load calculation?

Solar heat gain coefficients (SHGC) represent the amount of solar radiation that enters a building through windows and other fenestration. SHGC values range from 0 to 1, with lower values indicating less solar heat gain. The SHGC value depends on factors such as the type of glazing, frame material, and shading devices. Accurate estimation of SHGC values is crucial to ensure that the cooling system is sized correctly and to optimize energy efficiency. For example, a building with low-E glazing and external shading devices will have a lower SHGC value than one with single-pane glazing and no shading devices.

How do I account for occupancy schedules and time of day in cooling load calculation?

Occupancy schedules and time of day significantly impact the cooling load, as they influence the amount of heat gain and loss through the building envelope. To account for occupancy schedules and time of day, you can use various methods, including the bin method or the heat gain calculation method. These methods involve estimating the heat gain and loss during different periods of the day and adjusting the cooling load accordingly. For example, a building with a high occupancy rate during the day may require a higher cooling load than one with a low occupancy rate at night.