On Wed, 28 Jul 2004 11:08:09 GMT, "HeatMan" wrote:


"CBHVAC" wrote in message
...

"HeatMan" wrote in message
link.net...
Ever heard of a remote condenser??


Gee...and all these resturants must be obsolete..

Hey, if the Bride would let me, I'd have a remote condenser for my HH
'fridge. Of course, it would be a commercial 'fridge too....



It's called a split system, and the design is completely different.

The trouble with moving the HS (high side) of your domestic unit outdoors in
cool weather is in the projected enthalpy gain on the LS (low side) vs the
anticipated compressor run time [very indirectly, but not necessarily, its
duty cycle].

Specifically, it is designed to cool the freezer by running the pump
(compressor) long enough to reach design temperature, with everything in the
freezer section frozen, while the refrigerator section remains at equilibrium
with the ambient [kitchen air temp] to maintain 0 to 4 deg C, withstanding the
heat gain via the walls, door seal, etc. The heat gain [through imperfect
insulation] is actually =necessary=, because the system has only one pump
(compressor) [and usually only one loop]. The heat gain, through the
insulation, provides for the pump cycling, and the freezer runs colder,
because most of the evaporator surface is in the freezer, and the freezer
space is usually smaller. Therefore, the ratio of cooling enthalpy to gain
through the walls is greater in the freezer section, and thus it will be at a
lower equilibrium temperature than the refrigerator.

But the condenser is designed for ambient temperature of room-temp, more or
less stable, +/- within 10 to 15 deg C or so. If ambient temperature falls
much below about 13 deg C (55 deg F), we have problems, sometimes severe,
as the unit struggles to maintain the differential between refer/freezer
compartments. Worse still, no simple adjustment will compensate, since
outdoor temperatures can fluctuate widely.

What happens? When air over condenser drops much below design parameters,
the system pressures also drop. At first, efficiency improves slightly,
but, as evaporator temperature continues to drop, the increased gradient
leads to increasingly accelerated heat loss into the evaporator. To prevent
everything in the refer compartment from freezing, the "cold control" shuts
the pump down. This is called "short-cycling". If severe enough, the pump
will simply not run long enough to keep the freezer cold enough, as the
temperature "split" (gradient) is too great between the refrigerant and the
refrigerated product/space. Furthermore, efficiency actually =suffers= at
this point, as well, because the LS is now running in a depression [partial
"vacuum"], rather than at a slight positive pressure. This translates to a
larger refrigerant vapor volume, but at a lower enthalpy. The trade-off in
duty cycle is seldom a wash, even though the run-time per cycle is quite
short. Short-cycling is seldom very efficient (proportional heating control
aside g).

Exhausting the condenser waste heat outdoors IS an option, but just don't
redirect the condenser air =supply= from outdoors, as well. Take that from
the room, and let make-up air from another room replace it. It is 200 or 300
watts of waste heat, on the average. In the winter, however, you WANT this
heat of compression. So, putting the HS outdoors is insidious. Don't do it,
unless you have a split system, and one specifically designed as such (usually
with TXV [aka TEV] metering). You'd be ****ing up a rope.






--
-john
wide-open at throttle dot info

~~~~~~~~
"The first step in intelligent tinkering is to
save all the parts." - Aldo Leopold
~~~~~~~~