The human body has its own heating, ventilating, and air conditioning plant. The epidermis, or skin, is its control system. Water, being available in abundance in the human body, is a natural means of storing heat or rejecting it. Remember science class in high school? Who remembers what percentage of the body is water? Wasn’t it some ridiculously high percentage? When we heard the teacher tell us, we all made kind of an unconscious mental note that that just couldn’t be. Nevertheless, when the human body needs warmth, the pores of the skin close up or constrict, hence the body retains moisture and stays warmer. When the body needs to be cooled, the pores open up, allowing moisture to escape in the form of perspiration. As the perspiration evaporates, heat is removed from the body and we feel cooler. Evaporation requires one of two elements: either the surrounding air must be dry (we call it low humidity) or it must be moving. If either exists, evaporation can occur. In the old days, all cooling was by ventilation and it occurred by means of evaporation. That’s why a convertible in the heat of summer can still be comfortable, even though the temperature is 95 degrees. We do not feel hot because, at 75 miles per hour, there are plenty of breezes to cause the evaporation we need to feel cool... unless, of course, we are parked on the expressway during rush hour.
To further complicate the matter, remember the song, “Hey 98.6, it’s good to have you back again?” Well, 98.6 is the temperature of a normal human body. Right? ___ Wrong? It’s the temperature of the national average normal human body. My normal is 96.4. Yours might be 98.9 or even 100. Nurses today consider any temperature from 96-100 to be normal.
My wife says she can detect a 1 degree temperature difference. In the winter, at 67 she is comfortable, but if I try to inch the thermostat down to 65 for my comfort and to save energy, she asks when the last time was I heard the furnace run. If the human body can have a normal temperature from 96-100, then you can design the perfect HVAC system to keep someone with a normal temperature of 98.6 comfortable. But others in the same space could be too hot or too cold by as much as 2.6 degrees.
Another issue is the response time of our HVAC systems. There is a lag time built in to our control systems. It could be anywhere from 5 to 10 minutes long, or it may be defined in degrees (3 to 5 degrees, give and take). No commercially available system can hold a temperature right on the money at the set point. Not even direct digital control systems can do that. Years ago, when I worked for Clark, Tribble, Harris, and Li, I worked with an engineer who told me about a Belk’s department store job he did. Belk’s is the Southern version of Macy’s. The building was completed and occupied. On opening day, everyone was pleased with the job. However, shortly after it was occupied, certain employees began complaining about the temperatures in the space. My friend sent the contractor back in to verify that the system was balanced. He discovered that it was all out of whack, so he re-balanced the system at his expense. Furthermore, he installed locking covers over the thermostats to prevent tampering. He left and all were happy. Soon, the same complaints started again, and the contractor was called for service again. He checked and found the system out of balance again. It seems that in the morning, when the ladies would start their shift, they would be chilly so they would adjust the thermostat on the pole nearest them upward. In an adjacent department would be a man who was warm so he turned the thermostat down. It didn’t take long to throw the system out. This time the contractor re-balanced the system, but relocated the real thermostats to the ceiling, about 20 feet in the air. He installed dummy thermostats on EVERY pole in the space. And that ended the complaints. Everyone would adjust their thermostats and swear that the temperature improved immediately.
Let’s talk about comfort in schools. How do we achieve comfort in our various types of spaces in a school? First off, what is comfort? Comfort is sometimes defined as the body being at equilibrium with its surroundings. It is not too hot and it is not too cold. It is just right. For your information, just right is comprised of two components, temperature and humidity. In our HVAC business, we are always fooling around with these two elements. In oversimplified terms, we reduce the indoor temperature to be lower than the outdoor temperature and remove humidity from the air to give the occupants of the space the feeling of comfort in the summer. We increase the indoor temperature to be higher than the outdoor temperature to give the feeling of comfort in the winter.
OK, that’s the basic concept. Now, enter in reality.
In reality, there are over 400 variables which enter into the design of an HVAC system for any space. Things like the direction a room faces; how much glass is on an outside wall; whether or not the glass is tinted, reflective, thermo pane, or 1/4 inch thick; what the emissivity of the glass is; how many people will occupy the space; what their level of activity is; what pollutants are present that need to be diluted or expelled; what percentage of outside air is required for ventilation; how much money is available for the systems; where the systems can be located; what finishes will be in a space; whether the finishes should be included in the calculations or ignored; what insulation is in the walls, ceiling, and roof; what kind of walls the space has; what kind of system should be used; what the area of the walls and windows are; whether or not we have a plenum return or all the walls go to the deck; how many coffee pots will be in the space; how many computers will be in the space; what other pieces of equipment which give off either heat or moisture will be in the space; how much space is available between the ceiling and the roof or underside of the next floor; and on... and on.... and on.
If people leave a space for any reason, how long will they be gone (take for example the theatre or elementary school recesses)? In a sports complex, will the facility be used for purposes other than sporting events? In reality, the single most important element in designing a system for the comfort of a space is the glass. What direction will the glass face; what is the area of the glass; what direction does it face; what’s its emissivity,color, air space, and reflectiveness? The two most important elements of the glass are the direction it faces and its area.
In reality, it is impossible to design a space so that everyone will always be comfortable. What choices must be made regarding comfort? Usually, in a group of offices, we select the location of the system control based on supposed importance of the space. The superintendent of schools gets the controlling thermostat in his office. So, he is comfortable, but if he is in an office full of women, they may not be. Because he is the superintendent, you architects give him a corner office with two exposures and a window on each! Then, to make matters worse, the windows face South and West. The mechanical department head’s office in a company I used to work for is a good example. He had South and West facing glass. Year-round he used a portable fan to keep his space bearable. Some architect gave this building an abundance of glass. Do we have the pleasure of looking outside through the abundance of glass? Nope, it’s too hot, so we keep the blinds closed all the time on sunny days when you would enjoy looking out or getting natural light. The other factor for us is glare on the computer screens. Again, less glass would be better. In the case of the superintendent, we oversize the air conditioning to meet his need and it is too large for the rest of the space, so it overcools the women in the other offices with just south glass or no glass at all. In addition, his office is under a sloping roof, so we can’t locate the unit serving his space close to his office, and everyone knows the space closest to the unit gets satisfied first, the one furthest away last, and so on and so forth. He cranks the system up so that he, the furthest office from the equipment, is comfortable, and the other offices again freeze. Oh, you say, just give everyone their own unit and then they can have whatever they want. Unfortunately, no client wants room air conditioners hanging out of every window, and neither do you architects, but that would be what it would take to do what you ask. What we do is make a series of compromises for the best overall system, knowing full well that you cannot please all of the people all of the time.
With all of this in mind, we do a pretty good job of keeping up with you architects and providing a comfortable space for your clients, but here are a few things for you to keep in mind as you are laying out the proposed spaces for your clients.
1. Minimize the South and West facing glass.
2. Minimize the South and West facing glass.
3. Minimize the South and West facing glass.
4. Minimize the South and West facing glass.
5. Minimize the South and West facing glass.
If you must have abundance of glass, let it be in the preferred northern direction. Try to locate the big cahoona’s office on the North side or with enough overhangs to shade his windows. If this is still not possible, then figure that no matter what you do, your building will waste energy, will not be LEED certifiable, and will be excessively uncomfortable.
The heating issue is similar; if you use large expanses of glass on outside walls, then we must have the space and finances to provide a perimeter heating system in addition to the regular system. Here, we want to minimize the North facing glass, because there is no heat gained from the sun in the winter on the North side of a building.
Finally, let’s talk about what each school employee expects in the new school from an HVAC point of view. The room which was too hot before because of an uncontrollable, antiquated steam heating system may be too cold now because of too much glass on a North wall and no perimeter heating system. The room which was cooled by a room air conditioner before, which was too noisy and unevenly distributed the comfortable temperatures, may again be adversely affected by too much glass on a West wall. The employees expect all their gripes about the old school to be rectified, because this is a new building and they’ve spent a lot of money for it. We know it is impossible to fix all of the gripes. We will give them the best available comfortable system for the money they have to spend. We will do our utmost to see to it that we give them the best components, the best design, the best construction, the best of everything within our control. We will endeavor to give them a design that individually addresses their needs. But, if we fail to address their comfort in the new space, no matter how much effort we have put in and no matter how elated we are when the job finally goes out, we have failed. We must endeavor to meet all of the client’s needs. This means not only providing a space which is aesthetically pleasing, but functional, LEED certified, economical, and comfortable as well.
So, in closing, minimize the glass wherever possible OR provide extra dollars for mechanical system construction and operating costs.
Robert graduated in 1972 from the University of Cincinnati with a bachelor's degree in Mechanical Engineering in the Urban Option. He also completed The Little Red Schoolhouse training course by Bell and Gossett and both Trane's and Carrier's HVAC design courses. He has been working proactively as an engineering designer for over 35 years, performing research in facility energy analyses, water quality studies, air quality analyses, and performance studies. In addition, his intuitive abilities to determine the causes of malfunctions have been repeatedly demonstrated. He was the project manager on a massive study of 26 of Ohio's reserve military bases to determine every instant of cross-connection and recommend its remediation. His designs have included HVAC, plumbing, irrigation, fountain design, and fire protection and his experience encompasses commercial, educational, government, health care, and industrial facilities.