|
Geoff McDonell
P.Eng. LEED̉
AP
Climate Zones
Copyright (c) 2005,
Building Science Corporation
The Comfort
Calculator developed by
Dr. A. Marsh and the guys at
Square One
Research PTY LTD...is
for you - go ahead, click the picture above...play
with the humidity and see what happens.
|
The
Complete Comfort System
By
Geoff McDonell
P.Eng. LEED
(R)AP
Copyright (c) 2005, All Rights Reserved
What is a total home comfort system? Well, depending on who
you ask, it can be many things, from the aesthetics of a space,
to simply good indoor temperature control. Given that the
biggest source of indoor comfort complaints stem from being too
hot or too cold, from a pure human thermal comfort point of
view, I think a total comfort system for a house (or any other
building) must consist of a system that maintains comfortable
temperatures, provides good ventilation, and humidity control
all at the same time.
Many scientific studies of human comfort factors have all
shown that human thermal comfort is affected by three main
factors:
40%-50% radiation heat exchange
35%-40% air movement/air velocity
10%-15% humidity/perspiration rate.
Unfortunately, almost all of the common home heating systems
provide only half of the human comfort factors- air movement,
and sometimes indoor humidity control. Gas–fired furnaces just
move warm air around, and if you’re lucky it will be equipped
with a rudimentary humidifier for those dry winters. Electric or
hot water baseboards heat low level room air and create rising
plumes of warm air that eventually heat up a room, and there is
NO possibility of adding humidification to a system like that
unless you count placing open saucers of water on the radiators.
The baseboard heating systems don’t even provide ANY amount of
controlled outdoor air for ventilation, so only a very small
portion of the comfort factors can ever be provided.
The common theme around all of the conventional home comfort
controls systems sold today are: use a lot of hot and cold air,
and blow it around a lot to make up for the “fast acting”
thermal loads in the house. What’s the problem? They generally
all work OK, and keep the interior of a house at reasonably
comfortable temperatures, right? Well, it takes a lot of energy
($$) to heat and cool air, and blow it around. That HVAC system
operation is reacting to whatever happens outside the house -
hot sunny climates, cold winters, sun disappearing behind a
cloud and coming back out, and so on. This creates a fluctuating
comfort system, always trying to catch up with the thermal
variations. A better designed house envelope (walls, roof,
windows) reduces, and can often eliminate these “fast acting”
thermal load variations, allowing the indoor comfort levels to
be maintained with very small heating and cooling systems, and a
very stable indoor climate can result.
So, how do we get a low energy, total comfort system? It
starts with the house envelope design. Keep the climate
variations outside, and the interior of the house becomes a much
more stable climate, that needs less energy to maintain comfort.
Then, design a home heating/cooling system that provides all of
the human comfort elements – radiant comfort, good ventilation,
and humidity control.
In a heating dominated climate like most of Canada, a radiant
heating system, and an air to air heat exchanger ventilator with
added humidification would be appropriate. Some climate zones in
central Canada will also need de-humidification, and possibly
cooling in the summertime. Similarly in the United States, the
many climate zones will require variations on the system
depending on the house location.
The ideal home comfort system must have a radiant temperature
control system using either radiant floor heating, or combined
ceiling radiant heating/cooling, a ventilator to provide healthy
air changes, and in the climates that require it, a humidifier
for wintertime, and a dehumidifier for summertime. If a radiant
cooling system is used, the de-humidification is certainly a
“must have” to insure that the radiant cooling system can
operate free of condensation at extreme conditions. Opening
windows are also something that can be easily integrated into
the total comfort system. Using natural ventilation to
supplement the powered ventilation system during spring and fall
conditions helps to save energy, and provides another “control
point” in the room for comfort maintenance.
Is this kind of system expensive? Yes, the combined radiant,
powered ventilation, and humidity control probably costs more
than slapping in a furnace or a packaged air conditioner, but at
what price do you set your comfort tolerance? If you’ve spent
the building costs in the right places, starting with the
envelope and windows, then your heating and cooling needs are
minimized, requiring smaller heating/cooling appliances anyway.
It’s all about cost shifting- spend more on the envelope to save
on the heating, ventilating and air conditioning systems. The
total house costs are still going to be relatively the same if
you compare it against a conventional house approach. A small
hydronic radiant system and an air to air heat/energy recovery
ventilator also takes up a lot less space in the house compared
to the furnace and ductwork, or air conditioner and ductwork
systems, and saves energy costs for the life of the house.
Hydronic heating and cooling coils can be added to the
ventilator ducts for additional room by room fine-tuning control
as well. So what would the cooling source be for the warm
climate “total comfort systems”? Water to water geothermal
systems and small air cooled water chillers are the most common
solutions. While these systems might be thought of as
“expensive” or “premium” equipment, remember that the sizes and
capacities of this type of equipment can be minimized by the
better house envelope design that reduces the heating and
cooling loads to as low as possible in the first place.
A properly designed total comfort system will provide the
best indoor air quality, thermal comfort, and low energy
consumption for the life of the building. The interior
aesthetics can also be factored into your “complete comfort”
once that total thermal comfort system is done.
- Geoff McDonell P.Eng. LEED® AP
REFERENCES:
http://www.support.caed.asu.edu
http://www.squ1.com/index.php?
http://www.squ1.com/passive/passive.html
http://irc.nrc-cnrc.gc.ca/cbd/cbd102e.html
http://peakstoprairies.org/p2bande/construction/contrguide/section4.cfm
|
