I'd do the comparison against one of the much cheaper energy star rated
AC models. In my comparisons,On the slight edge in efficiency isn't
worth the extra cost of the DC units. I've also had premature failures
of DC fridges due to low voltage. Finally using the inverter's built in
low voltage disco keeps the batteries from getting ruined if the charge
system is down, but loads stay on.
I lived for years with a DC fridge, and my family has no desire to go back.
Ray Walters
12/11/2012 12:54 PM, Jason Lerner wrote:
Hello Larry,
I still install DC fridge/freezers in off grid systems for efficiency,
but also so that when the owners leave for the weekend/week/month
they can turn off the inverter and all the associated phantom AC
loads, but the DC freezer is still on. When they come back, the meat
in the freezer is still frozen.
Recently for a new off grid cabin we compared a Subzero 23 Cu. ft.
fridge/freezer to a Sundanzer chest freezer and Sunfrost all fridge
which is 51 cu ft.combined. Using nameplate yearly KWH's, retail
price tags and putting the freezer in an outbuilding we found the
sunfrost/sundanzer has 2.22 times more cu ft at 60% of the subzero's
energy consumption....at 66% of the cost of the Subzero.
Adding additional PV/wiring/CC/racking to run the Subzero was going to
cost an additional $2500. The contractor building the cabin brought
up the point that the Sunfrost does stick out farther into the kitchen
then an "average" fridge and there was going to be a cost associated
with custom cabinets to match that depth, possibly the same amount as
adding extra PV's...
Best,
Jason Lerner
Waldron Power and Light Co.
On Dec 11, 2012, at 10:55 AM, Larry Crutcher, Starlight Solar Power
Systems wrote:
Why would one specify DC voltage appliances or lighting for off grid
systems today when we have sub-buck-a-Watt PV solar power? If you
have space, you can make the added power that conventional AC
appliances draw for very low cost. It could even be argued that the
cost for DC items, wiring, distribution gear and labor will cost much
more than simply adding more PV solar and staying all AC.
I don't like wasting resources and I understand old school thinking
when PV modules were very expensive, but with high efficiency AC
appliances and low cost inverters and PV modules, does it still make
any sense? Shine some light on my thinking.
Larry Crutcher
Starlight Solar Power Systems
On Dec 10, 2012, at 9:12 PM, Allan Sindelar wrote:
Wrenches,
We still try to encourage prospective off grid customers to do a full
load analysis as an initial step in the system design process. To the
point:
1) What is a good watt-hours/day figure to use for a typical, modern,
new, carefully chosen, fairly large conventional AC chest freezer, if
kept in a heated indoor location? Assume 65 degrees and seldom opened.
I will encourage that the freezer be located in a shaded, protected
outdoor location, in order to greatly reduce winter energy
consumption, but I need a good base figure to work with.
The proposed system will most likely be 48Vnom, so a Sundanzer or
similar DC freezer is out.
2) Same question for a ceiling fan, for general slow circulation of
winter heat. The energystar.gov <http://energystar.gov/> list gives
relative cfm efficiency but not wattages. Is 55W still a good figure
to use as a default?
I have attached a condensed energystar.gov <http://energystar.gov/>
list for the freezers, but wonder what other off grid Wrenches
typically use. Also, I'm not sure that Wrenches posts allow
attachments, so this may not appear with my message.
Thank you,
Allan
--
*Allan Sindelar*
_Allan@positiveenergysolar.com_ <mailto:al...@positiveenergysolar.com>
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
*Positive Energy, Inc.*
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
*505 424-1112*
_www.positiveenergysolar.com_ <http://www.positiveenergysolar.com/>
*
*
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