What impacts HVAC operation cost

Houston HVAC companies design HVAC systems keeping in view the hot and humid weather. It is necessary that all the factors are taken into account while designing the HVAC system. Internal and external thermal loads play a major part in determining the type of system designers select and the Houston HVAC Contractors install on site. The primary function of the HVAC system is to reverse heat gain and heat loss in summer and winter respectively. So what are the factors that drive these internal and external thermal loads? Let’s take a look at them.

As shown in the image above, during the summers i.e. when the building is in cooling mode, the external heat gain (it is termed as heat gain as the outside temperature is higher during summers as compared to interior space and heat flows from outside to inside) into the space is mainly through the walls, roof, glass and air infiltration. While the internal heat gains are represented by the heat radiated by the activity levels of people, lights and equipments within the space. Now a distinction has to be made between sensible heat gain and latent heat gain.

Sensible heat: When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat. Heat that causes a change in temperature in an object is called sensible heat.

Latent heat: All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor) but changes such as these require the addition or removal of heat. The heat that causes these changes is called latent heat. Latent heat however, does not affect the temperature of a substance – for example, water remains at 100°C while boiling. The heat added to keep the water boiling is latent heat. Heat that causes a change of state with no change in temperature is called latent heat.

So the HVAC system works to counter both sensible and latent heat gains into the space during summers and heat losses during winters. Higher the heat gains or losses, higher the HVAC operational costs. Therefore it makes sense to reduce these heat gains/losses.

The heat gains/losses through the roof and walls can be reduced by adding adequate insulation and having light color paints on the exterior. By selecting a glass with low Solar Coefficient (SC), the heat gains can be minimized during summers but it would have a negative impact in winters where you would want to have more solar heat coming in through the glass. Properly sealing the gaps can reduce the air infiltration. Using Energy Star rated equipments, installing LED lights, automatic lighting controls can help in reducing the internal heat gain.

A compromise has to be achieved between cooling and heating energy of HVAC systems and the Houston HVAC companies know this the best.