From fireplaces to thermostats in less than seventy years!
ethods for warming people have
come a long way in a relatively
short time. The historical
progress from open fires in
caves, through fireplaces and wood stoves to
gravity warm air systems was dramatic. It
was the advent of steam and gravity hot
water heating boilers in the 1890’s that
made central heating systems possible.
Then came the modern hot water boiler with
copper fin baseboard (circa 1947) which
made for convenience beyond people’s
wildest dreams. Just think about it – from
fireplace to thermostats in less than seventy
years! It was a fantastic period in our
There is more innovation to be had beyond
the technology of 1947. We can learn about
what lies ahead by exploring some of the
basic principles of comfort and heating.
Every major industry continues to
innovate: the computer industry, the
automobile, the kitchen appliance. (Can you
imagine Ben Franklin working with a
Cuisinart? He’d wish he had never
discovered electricity!) To help you keep
your share of the market that is looking for
comfort and innovation, here are some basic
and very general rules for your review.
Heat always goes to cold.
U nder normal conditions, the human
body maintains an internal temperature
around 98 degrees with 70 degree skin
temperature. If we lose heat too quickly to a
colder space, the blood vessels constrict,
thus reducing blood flow to our hands, feet
and heads, and we shiver. If it’s too warm
and our bodies can’t shed heat fast enough,
we start to sweat. Thus, we should not be
trying to lightly “toast” the human body.
What we should be doing is controlling how
much of our body heat goes to cold.
In other words, we are not trying to
heat or cool the human body; it can do that
it’s self. We are controlling the external
factors that would pull the heat from us or
put too much in us. There are six factors
that determine human comfort: air
temperature, air velocity, relative humidity,
radiant environment activity level and
insulating value of clothing. Most people
tend to think only about air temperature. In
fact, it seems as though some people don’t
know if they are comfortable unless they
look at the thermostat. That doesn’t tell the
whole story. If air were blowing across our
body in winter, we might want our
environment to be 74 degrees to be
comfortable. In a radiant environment, we
might feel extremely comfortable at 68
degrees. In the low relative humidity of
winter, an even higher air temperature might
be required for comfort in both of
these cases. There certainly is more to this
than setting the thermostat at 70 degrees!
Heat Loss changes all winter.
W hen the outside air temperature
drops below 68 degrees, Principle One kicks
in with heat trying to get from hot (inside) to
cold (outside). This amount of heat loss,
changes from day to day and even hour to
hour, all season long according to the
difference between inside and outside
temperature. Engineers call this difference
Delta T or (Temperature Difference).
The traditional approach for sizing
heating equipment has been to determine the
coldest weather you would ever expect
(design conditions), add a safety factor,
some pixie dust and one more boiler section.
The end result is a boiler that is probably
oversized by a lot the rest of the season.
Ideally, we should have a boiler that changes
size with the weather. Think about this: if
you design for optimum system efficiency,
the boiler would never shut off on the
coldest day of the year.