Sv thermodynamics pdf

To understand how a Solarventi & Sensible heat works, let us give you some background insight.

“SENSIBLE HEAT is the heat absorbed or given off by a substance that is NOT in the process of changing its physical state. Sensible heat can be sensed, or measured, with a thermometer, and the addition or removal of sensible heat will always cause a change in the temperature of the substance. Heat flows only from objects of higher temperature to objects of lower temperature. This was described earlier as the natural flow of heat. When two objects at different temperatures are placed near each other, heat will flow from the warmer object to the cooler one until both objects are at the same temperature. Heat flows at a greater rate when there is a large temperature difference. As the temperature difference approaches zero, the rate of heat flow also approaches zero. Heat transfer will occur between two materials of different temperature” Note # The heat source is the sun sending heat via a Solarventi into your house, being the (heat sink) absorber.

Energy is the driving force for the universe. Energy is a quantitative property of a system, which may be kinetic, potential, or other in form. One form of energy can be transferred to another form. Heat is the thermal energy transported from one system to another because of a temperature difference. The transfer of that energy stops when the temperature balances out in the entire environment. The laws of thermodynamics govern how and why energy is transferred.

Second law of thermodynamics simply stated this – heat always flows naturally from an object at a higher temperature to an object at a lower temperature, and heat doesn’t flow in the opposite direction of its own accord.

The law is certainly borne out in everyday observation — when was the last time you noticed an object getting colder than its surroundings unless another object was doing some kind of work? You can force heat to flow away from an object when it would naturally flow into it if you do some work — as with refrigerators or air conditioners — but heat doesn’t go in that direction by itself.

A reversible process , is a process that can be reversed through tiny changes, without a dissipation of energy, i.e. the heat sink (walls, floors, structure) release the heat back into the air overnight or on cloudy days.

Background Heat flow can be a transient or a steady process. In the transient state, temperature and/or heat flow vary with time. Steady-state heat flow occurs when the temperature and heat flow reach a stable equilibrium condition that does not vary with time.

Heat flow can occur in one, two, or three dimensions. In almost all real situations, heat flow occurs in three dimensions acting alone or in some combination: ▪ conduction - convection – and radiation.

Changes in moisture state, although not strictly an energy transfer mechanism, must also be considered since these state changes absorb and release heat energy, i.e., latent heat.

Conduction is the flow of heat through a material by direct molecular contact. This contact occurs within a material or through two materials in contact. It is the most important heat transport mode for solids.

Convection is the transfer of heat by the movement or flow of molecules (liquid or gas) with a change in their heat content.

Radiation is the transfer of heat by electromagnetic waves through a gas or vacuum. Heat transfer by this mode therefore requires a line of sight connection between the surfaces involved. All objects above absolute zero radiate heat energy; it is the net radiative heat transfer that is the heat of interest. Radiation is mostly of importance for heat transfer between solids, but radiation between high-temperature gases (air) is of practical importance.

State change, sometimes called phase change, occurs at a constant temperature but still entails the movement of energy. For example, evaporation absorbs energy and condensation releases energy. This energy is sometimes called latent heat.

The mode of heat transfer often changes during the process of heat flow through and within building systems. For example, the sun transmits heat by radiation to the earth, where it can be absorbed, for example, by a black filter mat (Solarventi). The heat is then transferred by conduction through the filter mat and transferred to the indoor space by convection (Fan) and to the indoor surfaces.

Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation.

Thermal comfort is maintained when the heat generated by human metabolism is allowed to dissipate, thus maintaining thermal equilibrium with the surroundings. It has been long recognized that the sensation of feeling hot or cold is not just dependent on air temperature alone.

The recommended temperature range to optimise indoor thermal comfort for most people is 19°C to 28°C*.

The most important environmental factors contributing to thermal comfort are :▪ air temperature ▪ radiant temperature (ie. the temperature of the walls, floor, windows etc) ▪ humidity ▪ the amount of physical activity ▪ the amount and type of clothing worn.

Humidity- A house and its structure being a moisture sink in respect that if the humidity in the air goes up, then the house will absorb that extra water from the air. On continual basis, this will lead to the point of whole house/room saturation whereby condensation on surfaces is the result of the excess moisture.

‘Now we know a Solarventi works and why it works best.’

Eamon Corless.