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QUESTION:When lubricating furnace motor (Emerson F55HX CBR-1216 RPM 1075/3SPD)
The oil (Special blend for motors >1/4HP) leaks out of bearings.
1 IS it normal or should I get a spare motor soon?
(The motors runs smooth and quiet so the bearings are still OK but maybe
seal is gone.)
2 IS replacement of bearings cost effective?
3 I would like to change the control and use the other leg of the SPDT
contact that controls the fan to energize a low speed winding. Is it OK to
do it.
I realize that the fan will be ON all the time Medium speed when
heating/cooling and Low speed afterwards.
4 Eventually I would like to incorporate a cycler in the low speed control.
Do you know of any "of the shelf" cycler suitable for that. (Home Depot
stuff)
5. Ideally the cycler would be outside temperature modified.
(the cooler it gets the longer the ON cycle)
Am I pushing now or is there something on the market that would do the job?
ANSWER: Running the fan constantly during cooling days is recommended practice for
reducing air conditioning costs -
1. maintaining an airflow of 15 fpm across the occupants (ASHRAE standard for
AC) creates natural occupant cooling and minimizes stratification, and thus
will allow the AC to be set several degrees higher temperature with the same
comfort level than can a stop-start system.
In northern climes, where the dual-purpose registers are installed near the
floor, start-stop will definitely cause stratification and a layer of cold air
pooling at the floor.
2. In insulated structures, the cooling air being run across the walls
reduces the wall and furnishings mass temperature in off-peak times and has a
thrombic wall effect (the AC can "store up" heat removal and tap into it to
reduce total need on the unit during the high load demand portions of the day)
3. Fan bearing wear is significantly less when constant-run than with
start-stop. The wear on a sleeve bearing comes primarily during start and stop,
when the pressure on the bearing from the shaft is unevenly distributed, and
when force is also higher due to the higher start-up torque of the motor and
stopping inertia of the squirrel cage and air mass, and when the shaft-bearing
oil film that is in place during running is no longer in place, since the shaft
is stopped. Wear being a fourth power effect of force, the net wear is
significantly more during stop-start
A constant-run unlubricated bronze bushing can be run indefinitely without
liquid lubrication if properly sized. Lubricant is rarely lost in constant run
applications (being kept in by capillary action) but does need to be
replenished in start-stop (it seeps out of the bearing-shaft interface during
the off time)
(If improper lubricant is used or the bearing is mis-sized, the oil will
oxidize and gum and then heat the bearing and squeek, and new oil will be
needed to clean off the old oil. Sintered bearings, commonly used in furnace
fans, have a low-oxidizing-oil reservoir in the sinter, and rarely if ever
need new oil.)
(Some studies hold that the current inrush and additional current used to
start the airmass in start-stop is approximately equal to the constant-run
current used in most residential heating)
4. In dwellings with basements, constant-run allows a constant slight positive
pressure to be kept in the basement, stopping moisture migration into the
basement - (stops damp basements), and the moving air scavenges any moisture
fromt eh baement (note- basement intake registers, if installed, need to be
closed to get
As to water being re-introduced -
1. the uncharged coils should reach ambient temperature in under a minute if
the fan is moving air and the compressor stopped.
Water collects on the coils due to condensation of water vapor (from within
the dwelling) because the coils are a lower temperature than the ambient air
temperature, due to the liquid charge evaporating at the cooling coil exchanger
- since the compressor is off and the coil has taken on the ambient air heat to
raise its own temperature to ambient, it will not collect more water from the
air within a minute after the compressor shuts off.
2. if running the fan causes the water in the pan to go back into the house,
the drain is plugged or improperly installed - any water in the pan should go
out the drain line first from gravity and secondly from a slightly positive
pressure in the ambient-temperature-side of the cooling-coil heat exchanger in
the plenum corners.
>In the heating system it makes a little more sense to run the fan all the
>time but not much. Those 3 speed fans aren't particularly efficient at any
>speed. Running it all the time can easily cost you $100 or MORE a year.
Constant running of a forced-air fan in the colder months in the north is much
more efficient than stop-start - partly from fan wear and running costs (see
above) and also from (see ASHRAE)
1. stratification - lower ambient temperatures can be used with the same
comfort level constant-run since the temperature gradient can be below the 1
degree f per foot that causes discomfort in most occupants
2. Local surfaces - "wall-washing" registers maintain heat on the outer walls
and allow the thermostat to be set as much as 5 degrees F lower with the same
comfort level as start-stop.
3. humidity levels can be kept up in comfort ranges since more air moves across
the transfer surface and since the air moves across sills and glass,
evaporating/subliming any moisture/ice that would otherwise collect at the same
humidity levels in a start-stop system.
with proper filters, the air in the dwelling is cleaner with constant-run,
adding life to draperies and minimizing swelling and shrinking of wood
furniture. The wood and the air quality are
As all installatioons are slightly different, one should check the use of
electricty and fuel in your particular situation, billing period on start-stop,
billing period on constant, start-stop, and then copsntant again - and
normalize the use against the number of degree days (cooling degree days)
needed for the period, as indicated on the fuel bill (or available from the
power comany), e.g, if you use 500 kw and 1000 ccf gas running constant in a
month needing 1000 degree days, thermostat set for comfort under constant
conditions, and the combined fuel-power costs were $100 that period, then
divide the combined cost by the degree days. The next billing period, the
start-stop one, do the same calculation and compare. Then if you have a higher
run than start-stop cost (poosible in the south in winter, or in the north in
summer) guesstimate the worth of the fan wear and basement dampness and see if
you should run constant all year, part year, or at all.
for more detailed info, see the ASHRAE manuals on HVAC
--- personally, my forced air furnace fan has run constantly since 1978, with
stops only to change the Aprilaire super-filters once a year and for "burner"
maintenance (igniter). The registers have wall washer type registers
My basement hasn't been damp since it went constant, my fuel bill is quite
low (lowest around here even though my house is bigger than most near here,
although some of that savings is attributable to the "old" Hi Eff Amana
furnace) and short sleeves in winter inside is not unusual. I have many large
e-glass windows, and outside of the 24" insulation in the attic, it has the
original 1960 insulation.
My AC is a 2 1/2 ton, 2 roof power vents, and they have done quite well at
keeping us at 78 F on even those days long 95 F 95% humidity days this summer
with incessant energy save switch-outs- (in the great room, I do change out the
winter wall washer registers for hi-throw cooling registers for summer use.)
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