Drake,
The best thing to minimize blower power draw will be two fold.
1. Get the smallest BTU furnace you are allowed to (with and ECM
blower). Since blowers are generally sized at a nominal CFM/BTU of heat
output. (Around 30CFM/ 1000BTU for the usual heat pump or 90+eff furnaces)
2. Minimize head loss in the duct system. Head loss has an exponential
effect on energy use as a whole (blower motor and fuel efficiency)
a. Bigger distribution ducts
b. metal duct for corners and turns (i.e use good fittings)
c. little to no flex duct unless for straight runs
i. flex
duct always well supported and pulled tight, little to no slack allowed in a
flex duct job.
d. Etc. Good read in this article, and the attached presentation
download:
https://www.energyvanguard.com/blog/secret-moving-air-quietly-through-your-d
uct-system
Not knowing the home layout and specs it hard to give specific advise on
that side, but those two items are big drivers on actual power needs for
blowers. But as you said, the furnace is there for insurance costs, not
primary heating.
Also, the unvented propane heater in a primary dwelling seems like a bad
idea to me. Is the home expected to be well sealed for air leaks? Blower
door tested, relatively well sealed would be a blower door number of less
than 2-3 ACH50 (air changes per hour @ a 50pascal pressure difference to the
outdoors), 1-1.5 is really good, and passive house is 0.6 and lower? Because
both the fireplace and the unvented heater could be bad news if that's the
case. Something you might want to see if you client is conscious of. (Not
sure how far you are getting involved in the home design Drake.)
With Regards,
Daniel Young,
NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90
From: RE-wrenches <[email protected]> On Behalf Of
Drake
Sent: Friday, August 24, 2018 4:52 PM
To: RE-wrenches <[email protected]>
Subject: Re: [RE-wrenches] Forced air Furnace
A wood stove heats the house, and will be the primary source of heat. An
un-vented propane wall heater is installed and can heat the small, earth
bermed, well insulated structure. A furnace will be a nice supplement, and
will quickly pay for itself in insurance savings. During even a moderately
cloudy day, it will be fine, but will not be used much on batteries. Still,
I'd like as efficient a model as possible.
If I can find a unit with a 400 W draw, like the one in our on grid house,
that would be adequate. The specifications I've found on the blower motors
are sketchy. I will likely need to order it on line (or take a trip to a
neighboring city), so reading the nameplates might not be so easy.
Does anyone know how to get accurate data on furnace blower motors?
Thanks,
Drake
At 01:59 PM 8/24/2018, you wrote:
Content-Type: multipart/alternative;
boundary="------------914ACDD867C6488AACA07365"
Content-Language: en-US
I always try to talk the client into hydronic heating with ECM drive
circulation pumps. They do make ECM drive blower motors that can be
retrofitted in some furnace systems. Overall, its just a bad combination
off grid: the worse the weather is the less PV production you have, and this
corresponds to the same time that the furnace is operating 12 hours/ night.
They are either running the generator a bunch, or waking up in the morning
to a cold house with the power off, and dead batteries. If its an AC
coupled system, they won't even have any PV production the next morning
either. This is another reason AC coupled is not a great idea, or at least
you need to always have some DC coupled PV as well, but I digress......
Ray Walters
Remote Solar
303 505-8760
On 8/23/18 5:43 PM, Dana wrote:
Drake,
All the conventional units I have amp clamped over the years are pushing
900-900+ watts per hour. I do not recommend them ever & to date I have never
found a lower wattage blower. I would assume that a permanent magnet motor
would fit this suggestion, but I have not found one.
For off grid I recommend: Radiant floor heat first and hot water base board
second long before hot air. Air is a better insulator than a heat transfer
agent.
The new ECM (electronically commutated motors) pump motors are basically at
DC permanent magnet motor power draws [Taco & Grundfoss] these days.
Best of luck with this one.
----------------------------------------------------------------------------
Dana Orzel Great Solar Works, Inc.
C - 208.721.7003 [email protected]
<mailto:[email protected]>
Idaho Contractor - # 028765 Idaho PV # 028374
NABCEP # 051112-136 www.solarwork.biz
<http://www.solarwork.biz>
"Responsible Technologies for Responsible People since 1988"
P Please consider the environment before printing this email.
From: RE-wrenches <mailto:[email protected]>
<[email protected]> On Behalf Of Drake
Sent: Thursday, August 23, 2018 2:37 PM
To: RE-wrenches <mailto:[email protected]>
<[email protected]>
Subject: [RE-wrenches] Forced air Furnace
Hello Wrenches,
What is the best choice for a propane, forced air furnace for an off grid
house? We would prefer one that doesn't have a phantom load, although the
transformer for the thermostat may not be avoidable. Low blower current
would be preferable. The furnace AC will be powered by a Magnum 4448 PAE.
Thank you,
Drake
Drake Chamberlin
Athens Electric LLC
OH License 44810
CO License 3773
NABCEP Certified Solar PV
740-448-7328
http://athens-electric.com/
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