DC Pumps [RE-wrenches]
Jeffrey Wolfe, Global Resources
global at sover.net
Sat Jun 30 13:29:26 PDT 2001
Hi Travis,
We look at heating systems as follows around here. The following numbers
are given for a new, moderately well insulated house, heating efficiently.
(Yes, I know, if they build a REALLY efficient house, why do they need a
big outside boiler? That's what I told them to, but there are some good
reasons, see below.)
Heating system electrical use:
Boiler controls / electronics (propane or gas) 125W when running, 5 W when
off, running 8 hrs per day (not ABSOLUTE worst case, but a good design
point so long as there is a backup generator.) So this is about 1090Wh/day
Zone Pump 85W, 10 hrs per day. (It does run when the boiler is off.) (This
can and should be replaced with multiple ElSid pumps at 10W.) 850Wh/day
Control valves. Varies can add similar load to another pump, or less.
Better to have a system with multiple ElSids and no zone valves.
So we get a "traditional" system with about a 2 kWh (low end with ElSids)
to 3 kWh (average) to 4 kWh (high end) use.
A NEW oil fired system will add about 125 W while running, to power the
pump and blower needed to atomize the liquid fuel. So this adds 1 kWh/day.
(an old oil fired boiler can easily use 750 W when running. Watch out for
these! Believe the burner motor nameplate. It's real.)
So we get a "traditional" system with about a 2 kWh (low end with ElSids)
to 3 kWh (average) to 4 kWh (high, although not highest) use.
A remote boiler needs to supply heat to a storage tank. With the storage
tank in the house, the pump only runs while the boiler runs. This is about
3 hours per day, except on the most severe weather. So this 85W pump adds
about another 300 Wh/day (with controls)
These folks have a 2 kW array, and so we're figuring in the depths of
winter, they can make about 5 kWh in a day, considering ALL
inefficiencies. If we can get the boiler system down to the 2 kWh end, then
this is a workable system, without excessive generator run.
Reasons these folks went with the Tarm boiler (not to be confused with an
"outdoor boiler" which is much less efficient, way more polluting, and
doesn't work as well.) are as follows:
It gets all fire wood dust debris, ashes, soot and smoke out of the
house.
It lets them fire a unit once (or at most twice) a day. With a radiant
floor system they can probably go for two days without firing (since they
can use the low tank water temperatures effectively), but would then need
to fire longer.
Greatly reduces the risk of house fire, an important consideration when
living way out in the country. These folks are quite close to a paved road
and power lines, but probably 15 to 20 minutes away from a fire truck
getting to what's left of their house.
Allows then to have a renewable source of heat, yet also allows them to
use radiant floor heating. While a wood stove is "cozy" (its what we use),
it cannot compare to a radiant floor.
So far as system size goes, we find two types of clients. Those with lots
of money and those without lots of money. A 2 kW system may be out of reach
for some, but probably half our clients can afford it. Why not let them
live an on-grid lifestyle if they want to and can afford it?
Jeff
----------
From: Travis Creswell, Ozark Solar[SMTP:ozsolar at ipa.net]
Reply To: RE-wrenches at topica.com
Sent: Saturday, June 30, 2001 9:15 AM
To: RE-wrenches at topica.com
Subject: Re: DC Pumps [RE-wrenches]
Morning Hugh,
Tell me more about this "inverter" device you speak of? Perhaps it rights
things that are upside down? How can that move hot water? Surely you will
explain more as I am only a simple hillbilly easily confused by such
technical terms.
but seriously..
Although it's not what you would think, hydronic heating systems tend to
use
a lot more electricity than an off grid house can regularly generate in the
winter. The outdoor boiler systems are designed to have the circ. pump run
24 hours/day. There is ways around that but it still runs over 12 hrs/day
when it's really cold. That's nearly 2 kWh's for regular AC pump. Even a
super efficient DC pump will need nearly 1000 watt hours/day The zone
pumps plus the transformers for controls easily consume another 2000 watt
hours a day. When does the system need the most electricity? The
shortest,
darkest coldest times of the year. So even with DC pumps the systems that
I've looked at doing were going to require regular generator run time (fed
to the inverter to charge the batteries to run the pumps) to come up with
the 3 or more kWh's for the hydronic system. That's 3 kWh's before the
first light bulb or any other load is turned on. In my area this last
December averaged 3.1 sun hrs per day. I don't know about others but for
me
a system that would produce over 3 kwh's in the winter is pretty big.
Jeffrey, how many watt hours are you calculating you are going to need to
run your hydronic system? What is the avg. winter sun hrs where this
system
is going?
Travis Creswell
Ozark Solar
----- Original Message -----
From: "hugh piggott" <hugh.piggott at enterprise.net>
To: <RE-wrenches at topica.com>
Sent: Saturday, June 30, 2001 1:45 AM
Subject: Re: DC Pumps [RE-wrenches]
> >I have been faced with this several times and the only solution that the
> >customer would buy was running the generator vs. paying gobs extra for
DC
> >pumps amd more zones becuuse of the small capacity of the DC pumps.
> >
> >Well I only had more questions and no answers.
>
> Isn't there a new-fangled gismo you can buy nowadays called an
'inverter'?
>
> Or am I missing something?
> --
> Hugh
>
> http://www.ScoraigWind.co.uk
>
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