Posted on 12/03/2009 3:18:36 PM PST by Bean Counter
Three years ago we installed an entire new heating and air conditioning system as the finishing touch on a major addition to our home. We improved and added on to our 1100 SF 25 year old ranch home, and ended up with about 2150 SF total, and the old heating system system that the house was built with was worn out and undersized.
We bought this house because it had forced air heat and A/C. That is actually a rare commodity up this way, in the land of the baseboard electric heater.
We tore out all of the old R-19 under-floor insulation, all of the old duct work and the old vapor barrier. We had the underside professionally re-insulated to R-31+, including all of the pipes, put down a complete new vapor barrier, and then installed the new heat and air conditioning flexible insulated ducting. We replaced the entire air handling unit and the old heat pump and went with A Honeywell control system and an Amana heat pump.
We opted for a split, zoned air handling system. When air leaves the plenum under the house, it goes into two separate zones via large control valves that open or shut as commanded by the Honeywell controller, and directs conditioned air into the front zone, the back zone, or both, depending on weather the 2 separate thermostats are calling for air or not.
We have a very efficient wood stove in the front room (zone 1) and when the back of the house (zone 2) calls for heat, it takes suction from the family room and distributes the heated air from the wood stove throughout the house. I shut the heat pump off at the circuit breaker when the stove is heated, and we keep the entire house very comfortable with just wood heat.
The heart of the new air handler, and a significant savings in power, is the low voltage (24 Volt DC) motor. It has three speeds, including a "circulate" mode that really helps keep the house at a very stable temp. Because it runs on low voltage DC, it uses a fraction of the power that a conventional AC fan motor uses, and is in fact the latest way that manufacturers have cut the power usage for home heating, after the heat pump.
The system also has a set of emergency heating coils that are powered by 220 V AC, and for that reason the blower unit has it's own 220 AC service. There is a large transformer on the front of the unit that steps 220 AC down and converts it to 24 V DC for use on the motor and the electronic control system.
However, if I could disconnect all of the high voltage components in the blower box, especially the emergency heaters (which have their own breakers inside the cabinet) I think I can power the motor and control system, including the two thermostats, off of a series of 12 volt car batteries, properly configured. That would give me a way to effectively distribute heat throughout the entire house.
The question is whether it would be worth it to try and power up the whole system and try to power up the thermostats, or just run jumpers directly to the proper leads for the motor?
I have an amazingly complete and very clear set of schematics for the entire system, and I think I'm on the right track here.
For clarity, I am also toying with the idea of building a 24 VDC axial-flux generator as well, so I am thinking long term here, and that is for a different rant...
Thoughts, suggestions, free advice, insults, and smart-assed remarks, as always, are all most welcome...
Cheers!!
Pshaw! It's all ball bearings now.
Actually, if you're going to run this system at 24 VDC for any length of time, you might be surprised at how large your required battery bank might be. What is the amps required to run everything you want to run?
I would just go straight to the motors. Keep it simple. You sure aren’t going to want less heat, and if you do, you can cut down on the fire.
Since the “whole system” consists of the 24v components and you will be disengaging the 220 supplied heaters, I can see no good reason why not.
If it were me, I would thinking about running all my power needs to a single connector that can be physically turned off or disconnected just to make it safer.
2 12 volt batteries in series, especially if they are deep cycle ones will run that fan for days.
I would be interested to see if it works out for you.
If you do not get a better answer than what I have given you, I will run this by my brother for a more definitive opinion.
Cheers,
knewshound
If so, these operate with plused DC, not straight DC like a battery.
Because it runs on low voltage DC, it uses a fraction of the power that a conventional AC fan motor uses, and is in fact the latest way that manufacturers have cut the power usage for home heating, after the heat pump.
Nope. Power (voltage x current) drives the motor. A lower voltage motor will require more current than a higher voltage one to move the same amount of air. You might have a very efficient motor, but then the issue is having a good motor, not having a low voltage DC motor.
Now the serious part. Get a multimeter and measure the current needed to drive the motor. If the motor has a horsepower rating you could get a ballpark figure of the current needed by muliplying the horsepower by 746 watts/HP and then dividing that by the 24 volt DC supply. That will be the lion's share of the current you need. I don't have figures at hand on how many amp-hours a car battery holds (I'm used to little batteries' milliamp-hour figures), but you should be able to look it up for the size of batteries you are thinking about using.
1.21 GIGAWATTS!!?!?!?
Thanks. After ball bearings, this was next thought in lieu of a 24 VDC axial-flux generator.
It may be a little overkill for 2400 square feet...
I concur with the advice that’s been given, you simply need to know the current requirements of your low voltage motor(s) in order to come up with even a back-of-envelope estimate.
Furnaces have long operated from 24 volt AC controls, so that part is fairly easy, the issue for most of us is the 110 or 220 volt AC motor that drives the blower. You may have an edge there because you wouldn’t need an inverter but power is power, and it still takes quite a lot to distribute air throughout the house.
But one possibility - and I stress that I’ve not seen this done or even an engineering analysis of it, just some speculation - is the use of a thermopile or thermoelectric generator (aka Seebeck effect) to generate DC from the heat source you have (wood stove). The US Army has developed thermoelectric fans that are available for $200 to circulate air inside tents:http://store.colemans.com/cart/us-gi-thermoelectric-fan-p-2315.html
My feeling is if you could generate enough power to move sufficient air, a battery backup for the rest of the system would be trivial.
Also when estimating capacity bear in mind the duty cycle, i.e. you probably won’t be circulating air 100% of the time. Similarily, wind, solar, etc used for recharging is definitely not available all the time either. Living alongside a stream with enough head to turn a 10KW hydro would solve all problems ;-)
Most all manufacturers us 24VAC control voltages, the VAC stands for VOLTS A/C, Not DC.
1. You will need a 24 VDC charger to charge the batteries, and/or keep them charged.
2. Batteries are highly likely to generate hydrogen when charging, and leaking small amounts of hydrogen at all times. You don't want hydrogen gas ANYWHERE NEAR an open flame source.
3. Whatever size battery you pick, remember that its amp-hour capacity is significantly reduced when the temperature is only 10 degrees above or below its optimum temperature environment.
4. Battery ratings degrade over time, so don't expect older batteries to run your components as long as newer ones.
Best of luck with your project!
AC not DC for controls?
Wow, thats odd.
I do a ton of process control stuff and everything works on DC for the relays, switches and controls. Naturally, anything that requires serious power is AC based.
If it is actually AC, good luck. The losses you will incur converting from DC to AC will kill your efficiency. Those batteries will not last long.
Cheers,
knewshound
We used a box fan to blow the warm air from the area heated by the wood stove to the back of the house.
**Providing 220 VAC for any prolonged length of time is a problem, even with a generator, because you only have so much fuel.**
How much wood you have available? You can run a gasoline generator off of wood gas.
I have wood. I’ve never heard of wood gas.
It was big in Europe to run automobiles during WWII instead of gasoline. The wood is heated with little oxygen and gases is driven out of it which can burn in gasoline motors. Not as much energy as gasoline but in places where wood is plentiful it has possibilities.
I have been thinking myself of getting an old dependable pickup and converting it if oil goes sky high.
Here is a link but if you google it you will find a lot more stuff.
http://www.motherearthnews.com/Energy-Matters/Wood-Gas-Generator.aspx
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