White Rodgers 1F85-277 Guía para resolver problemas descargar pdf (Pagina 120)

However when two units are installed side by side in the same area

and both units add up to less than 6 Tons, this is the case for using

one unit and zoning.

Anytime a contractor can install one unit versus two, or more, the

homeowner wins. Maintenance costs are cut with every unit saved.

Remember the maintenance of air ﬁlters, electronic air cleaners,

humidiﬁers, electrical requirements and the life expectancy of these

HVAC units as well, are unnecessary added costs that can be saved

by using one unit and zoning.

Another reason for using one larger unit with zoning is to economical-

ly obtain zoning and the highest efﬁciency HVAC equipment. Often

when multiple HVAC units are installed these units are typically on the

lower scale of efﬁciency. For heating this is an 80% efﬁcient furnace.

For cooling this is a 10 SEER air conditioning unit.

ZONING EFFICIENCY AND DOWNSIZING

The standard way of not living in your whole house all of the time and

mostly occupying one zone of the home at a time proves the need

for zoning. Zoning makes the use of the heating and cooling more

effective by only conditioning those zones being occupied or that may

need it. Therefore typically the majority of the time, even on a two

zone system only one zone is typically calling.

When this occurs the furnace and air conditioner is oversized in BTU

capacity when supplying only a single zone. Due to this many HVAC

Installers will downsize the heating and/or cooling units based upon

the use of zoning. On a two zone system this many not be recom-

mended, however when using 3 or more zones it is practical to

downsize to the next lower capacity unit.

An HVAC Unit should be sized to heat and cool the home at design

temperatures (the hottest days in summer and the coldest days in

winter). Realistically how often do design conditions occur. Of course

this depends upon where you live. In the milder climates downsizing

is much more of a possibility than in the severe heating climates of

Northern states or the southern cooling climates.

HVAC installers have been quite successful in going to the next

smaller size unit when using zoning. In many cases heating and cool-

ing units are often oversized, especially on older homes. Doing a heat

loss and heat gain calculation is very important in determining the

size of the heating and cooling unit. Once the loads are determined

for the overall structure, the affect that zoning will have on the overall

load can be determined. Seldom used zones such as basements

or extra bedroom loads can be looked at as not always needing

conditioning at the same time as more often used zones. In instances

where 3 or more zones are used may be advantageous to downsize

to the next smaller size of heating and cooling unit.

NOTE: There are times during extended periods at design tem-

peratures where it will take longer for the zones to satisfy as the

heating or cooling. It is important to note that some zones would

have to be adjusted in order to direct more BTUs to the more

important zones.

Down sizing while also increasing efﬁciency is often the best way

to go. When considering the alternative of using 2 separate lower

efﬁciency units in order to zone vs. one high efﬁciency unit with zone

damper system, the cost difference is negligible if not sometimes

less. Take for example the following scenario and price out the costs

comparison of the following example.

A 100,000BTU Home with 2 Zones.

Two Units @ 80% Efﬁciency vs. One Zoned 90% Efﬁciency

2Units 1 Unit

x 50,000 BTU Each (100,000 Total) x 90,000 BTU (Downsized)

x .8 (80% Efﬁciency) x .9 (90% Efﬁciency)

= 80,000BTU vs. = 81,000BTU

When you look at the two options you can still get more output, with

higher efﬁciency and still provide zoning. Combine this with the po-

tential utility rebates for the higher efﬁciency and that often offsets the

added cost of the zoning system. Even going to one 80,000BTU, 90%

efﬁciency unit will only decrease the total output by 10% . In milder

climates this can be an approach to lower HVAC installed costs when

quoting against the competition with 2 lower efﬁciency units.

Applying higher efﬁciency and zoning to cooling can also increase the

effectiveness of the cooling. Here again if utility rebates are offered

for the higher efﬁciency this can further offset the added cost of zon-

ing and possibly add other comfort options.

Typically the more zones you have the wider the diversity in the use

of the zones. This factor can help in downsizing the unit. Take for

example an exercise room that may only be used a hour or two a day.

The family recreation room that is only used for a few hours in the

evening and not when all are sleeping in the bedrooms or eating in

the kitchen dining room zones.

Zoning and high efﬁciency equipment can increase the overall energy

performance of your home and keep rising energy costs down to

manageable level.

ZONING

DESIGN

TECHNICAL HELP

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