Pt. II Intro to Energy Use & Basic Energy Principles

Basic Energy Principles

Heat as Energy

Heating, cooling, and lighting a building involves the addition or subtraction of heat. A basic understanding of physical principles of energy of transfer and storage is indispensable for low-or zero-net energy building designer.

What is Heat?

Heat is a form of energy that is particularly relevant to building designers. Its unit of measurement in the United States is the British thermal unit (Btu) , and all other countries, the joul (j). Heat flows direction-ally from hot to cold. The only exception occurs when mechanical energy is used to "pump" heat in the opposite direction. Without a temperature differential, there can be NO transfer of energy.

What is Sensible or Latent Heat?

Sensible heat is dry heat, the result of molecular vibration in a substance. Temperature is a measure of the average intensity of the molecular vibration in that substance and is calculated in degrees. Typically in Fahrenheit (F) in the United States and Celsius (C) or Kelvin (k).

EVERY MATERIAL ON EARTH ABOVE ABSOLUTE ZERO HAVE MOLECULAR VIBRATION!

Heat is a function of temperature and mass, the amount of matter in an object. Two blocks at a temperature of 50 degrees Fahrenheit, each 1 ft long in all three dimensions, could contain different amounts of heat depending upon the density and thus the mass of the object. A block of stone has more mass than an equally sized block made of corrugated card board or Styrofoam.

Latent heat is released or absorbed by a substance during a change of phase.

Example, from solid to liquid, liquid to gas, or vice versa

1 Btu is the amount of heat required to raise the temperature of a pound of water at 100 degrees Fahrenheit, the temperature will increase by 50 degrees Fahrenheit.

THERE IS A CLEAR AND DIRECT RELATIONSHIPS BETWEEN THE TEMPERATURE OF WATER AND ITS HEAT CONTENT EXCEPT AT THE POINT OF A CHANGE OF PHASE!

Breaking the molecular bonds and transforming a water molecule from a large amount of energy , especially when water reaches its highest boiling point. As the water evaporates and is transformed vapor, air temperature drops while the moisture content of the air increases. The total amount of heat remains the same . If the water vapor condenses back into a liquid, the latent energy absorbed from the air during evaporation is released as sensible heat.

The release or absorption of latent energy during change of phase is what makes possible steam heat and refrigeration systems. Absorption of sensible heat from the air through the induction of moisture is the principle behind evaporation cooling .Removal of latent heat through humidity control is central to air conditioning.

Heat Transfer

There are four primary methods of heat transfer in a building!

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