FUNDAMENTALS OF HEAT LOAD CALCULATIONS Part 1

What Causes Heat Loss Temperature difference Outside Inside

Overview Of Heat Loss What is heat loss? 2.What causes heat loss? 3.How is heat loss measured? 4.What affects the rate of heat loss?

What Is Heat Loss? Heat Loss: 1.Transmission losses 2.Infiltration losses

What Is Heat Loss Transmission Losses 1.Heat transferred through confining walls, glass, ceiling, floor or other surfaces. - ASHRAE Terminology of HVAC&R

What Is Heat Loss? Infiltration Losses 2.Energy required to warm outdoor air leaking in through cracks and crevices around doors and windows, or through open doors and windows, and through porous building materials. - ASHRAE Terminology of HVAC&R

The Human Heat Source Why do you wear a coat, scarf, gloves, long pants in winter and shorts and sandals in summer?

The Human Heat Source  How much heat?  Where does it go?  The human body creates heat.

 How much heat does the human body generate It Depends. What Activity? The activity engaged changed the “comfort level” in the conditioned environment. For example a basketball player in a gym vs. a researcher at a library. The Human Heat Source

 An office worker is estimated to give off 500 BTU/hr.

The Human Heat Source  The human body at rest roughly produces the same heat as a 100-watt light bulb.

-10 Winter In The North  No protection.  Any heat your body generates is transferred immediately to the surrounding COLD. IT’S SO COLD!!! -10

Winter In The North Ok. It’s getting a bit warmer.  Building a little box around yourself provides some insulation from the outside.  The heat from your body slowly warms the air in your space. EXCEPT…

-10 Winter In The North DRAT!  Since Nature hates imbalance, and since you don’t have enough insulation to sufficiently slow down the heat transfer, the heat leaves faster than your body’s ability to generate it.

-10 Winter In The North There! That Should Work.  You add a heat source to your space.  The temperature starts to go up.

-10 Winter In The North I just can’t afford this much energy.  The cost of a bigger fire starts to hit the pocketbook.  What can we do? Out-dated construction methods were based on cheap fuel. With energy costs going up, this method isn’t the smartest design.

-10 Winter In The North Awww. The thicker wall should slow Nature down! Using an appropriate combination of insulating materials and heat sources, we can finally achieve the desired temperature.

Winter In The North The point of maximizing the R-value of the shell is to slow down Nature’s tendency to equalize imbalance. If you can retain the heat, then you can reach your set- point without having to have an unnecessarily large heat source. The more insulation, the slower the heat loss and the smaller the heat source required at design temperatures. When IN = OUT the temperature remains constant.

Nature Hates Temperature Imbalance Example #1:  Set hot cup of coffee on a desk in a comfortable room. Come back in few hours. Is it still as hot as you left? Why not?  What happened to the “hot”?

Nature Hates Temperature Imbalance Example #2:  Set a glass of water with lots of ice on a desk in a comfortable room. Come back in few hours. Is it still as cold as you left?  Why not?  What happened to the “cold”?

Nature Hates Temperature Imbalance As the temperature of the contents gets closer to room temperature, the rate of heat transfer slows down. Why? The rate of transfer from hot to cold is relative to the temperature difference. As the two temperatures get closer to the same, the difference (∆T) is less, therefore the rate slows.

4 Things To Remember Hot goes to cold!!!!!!!! 2.Hot goes to cold at a rate relative to the temperature difference. 3.Radiant heat goes an infinite number of directions from the source. 4.Heat is lazy. It will follow the line of least resistance.