Backup system for oil boiler - is this realistic?

Interlude
Interlude Registered Users Posts: 8
Hi folks, been lurking a bit and learned a lot so far. As it stands right now, for power outages, I've been relying on a Honda EU2000 for my needs - powering my oil boiler and hot water heater, refrigerator, and a few energy-efficient lights. I do have it set up with an external marine fuel tank so that it can run a considerable amount of time, but in the interest of fuel efficiency as well as avoiding the need to run it overnight, I've been looking into some kind of setup that will power my oil burner via battery. Were it just me, I'd just throw on a heavier blanket, but with young kiddies in the house, it's not as much of an option.

According to the information printed on the machinery, the oil burner control draws 120V at 7.4 amps at full load (with a momentary surge of 22 amps at startup). The circulator pump draws another .7 amps at 115V. The oil hot water heater has an identical motor to the oil burner, but I can pass on running that via battery. Obviously the burner isn't running at all times, but runtime would depend heavily on how cold it is outside.

In my head, the batteries would be charged during the day when the generator is running. Or, if by some miracle the power needs aren't as high as I think, I would consider solar. My house is on Long Island, NY with a considerable southern exposure.

Is this realistic or am I talking about a hell of a lot of money and equipment?

Thanks!

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Backup system for oil boiler - is this realistic?

    Welcome to he forum.

    "A lot of money and equipment" is a relative term.

    Assuming the numbers are correct (and I wouldn't) then your start-up surge is (22 * 120) 2640 Watts. That would mean you need a pretty big pure sine inverter just to get the motor going. Something like an Outback VFX3648. That's $2,000 right there. Still interested?

    Battery sizing is a bit difficult because the furnace is thermostatically controlled, which means you can not easily predict the run time. But roughly 8 Amps @ 120 VAC is 960 Watts, so realistically you are looking at approximately 1 kW for 1/3 of the time or 8 hours: 8 kW hours. That is a lot of power to store up. On 48 VDC that would be 167 Amp hours used, or a minimal battery size of 334 Amp hours @ 48 VDC. Easily another $1,000 in batteries.

    Plus taking into consideration conversion efficiency and inverter draw it could need to be even larger. What is worse is that the little Honda will not do so well at recharging such a bank quickly, especially if asked to run the load at the same time. So to get that "quiet time" at night you might be in for another generator (EU2000i can be paralleled or you can go to a larger size). So there goes more money.

    Now, how often does the power go out and for how long? Before you go sinking $5,000 into a back-up system you need to know if it will be a worthwhile investment for you. Chances are it won't be. And the batteries will age and need replacing regardless of whether or not they are used.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Backup system for oil boiler - is this realistic?

    To add to Marc's comments... I would suggest you get a Kill-a-Watt type power meter and plug your emergency loads into the k-a-w and see how much energy you use in 24 hours.

    A small generator is probably the most cost efficient. And get a second Honda eu2000i for backup to your backup (reliable generator, but things happen).

    Yes, a battery bank+inverter+AC battery charger is just a large "UPS" system. You can use Utility power to recharge (depending on how long your outages are), a genset for 1-2 weeks, or even solar for multiple month outages.

    The smaller you keep the battery bank, the lower your costs will be (smaller batteries, less to replace every 3-5 years or so), smaller AC Charger, smaller AC genset, etc...

    A typical battery bank design for an off grid system would be to support the home over 2 days without power and a 50% maximum discharge.

    For an emergency backup system, probably enough battery bank to support the home for 10-12 hours, and use the genset (or grid power if restored) for the balance of the day.

    Once you have a good handle on your loads, it is a pretty easy set of calculations to give you a couple of different size battery banks and to figure out the costs--And what makes the most sense for your home.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Interlude
    Interlude Registered Users Posts: 8
    Re: Backup system for oil boiler - is this realistic?

    Thanks guys, really appreciate it. Another question if you don't mind - I'd like to build just a small UPS-like system to run some LED lamps and . Figure about 40w worth of stuff, run about 4-5 hours per day. I'd need a battery, charger, and inverter (or a charger/inverter but are any of those reasonably priced?). Any recommendations for this kind of setup?

    Also, I've seen numerous people recommend two 6v golf cart batteries in series as opposed to one 12v with the same amp hours, is there a reason for that? It would seem that one battery would be cheaper than two.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Backup system for oil boiler - is this realistic?

    Working backwards ...

    A 12 Volt battery with the same Watt hour capacity as the two 6 Volts would be physically the same size and therefor somewhat of a problem to move at about 120 lbs. You really don't want to parallel two smaller 12 Volt batteries to get the equivalent power. Here's a relevant bit about batteries:

    http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    If you want to run 40 Watts for 5 hours that's 200 Watt hours. You would only need a 100 Watt inverter for that peak load, and will not find an inverter-charger in such a small size. For the big (>2kW) systems they are reasonably priced. This Watt hour demand can easily be met on 12 Volts; less than 100 Amp hours would handle it without high depth of discharge (about 20 Amp hours is all it would really use).

    Note on the use of the K-A-W with your furnace; you'll have to interrupt the wiring and put in a plug and outlet with the meter in between in order to measure power usage.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Backup system for oil boiler - is this realistic?

    Batteries are pretty priced by weight and "quality"...

    6 volt 220 AH "golf cart" batteries are cheap and relatively rugged. They will not last "forever", but around 3-5 years or so. You can pay 2x more for "better batteries" and they will last around 2x longer.

    For first time solar folks, usually they kill their first or second battery bank with mistakes (forget to check water, too much or too little charging, too much loads, a load left on for a few days, etc.)... So, a "starter" bank of golf cart/cheaper batteries is usually easier on the wallet.

    Another issue for many folks--Solar RE batteries are generally some sort of Lead Acid--And literately can weigh a ton. Paralleling batteries is usually not a great idea (1 string is "ideal", 2-3 parallel strings is OK). So, to keep batteries a reasonable weight to wrestle down stairs, etc... You sometimes go with lower voltage batteries (6/4/2 volt) and higher AH rating to keep the batteries less than a couple hundred pounds each, but build out a large Amp*Hour rated back with 1-3 parallel strings of batteries.

    If you have the area (and the hoist) to handle fork lift batteries, you can get then 1,000-2,000 lbs at a time. Either is perfectly OK.

    You want deep cycle batteries, not starting or "marine" batteries for off grid solar and "cycling" applications. The other batteries will just not last that long in cycling service.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Backup system for oil boiler - is this realistic?

    7.4 amps seems very big for a "normal" modern oil burner. My roughly 10 year old Riello burner will start and run off a little TS-300 inverter.
    The motor is capacitor run, so is quite efficient. Unless you have a huge furnace, perhaps it's time for a new burner. Same with the water heater. Not many folks still heat their domestic hot water with oil unless they have a really big family and need really fast recovery. Too expensive.
  • Interlude
    Interlude Registered Users Posts: 8
    Re: Backup system for oil boiler - is this realistic?

    Thanks again. How's this pairing?

    http://www.solar-electric.com/tr3112vo100a.html - Battery, only 69 pounds for 100Ah, I think I can handle that.
    http://www.solar-electric.com/dls-30.html - 30A charger
    http://www.solar-electric.com/sa300wa12vos.html - 300w Inverter. Is Samlex worth the premium over an Amazon-type inverter like Whistler or Cobra?
  • Interlude
    Interlude Registered Users Posts: 8
    Re: Backup system for oil boiler - is this realistic?
    7.4 amps seems very big for a "normal" modern oil burner. My roughly 10 year old Riello burner will start and run off a little TS-300 inverter.
    The motor is capacitor run, so is quite efficient. Unless you have a huge furnace, perhaps it's time for a new burner. Same with the water heater. Not many folks still heat their domestic hot water with oil unless they have a really big family and need really fast recovery. Too expensive.
    Here's a picture I took of the motor - perhaps I'm reading it wrong (sorry it's blurry)?

    The equipment was put in about 8 years ago by the prior owner. I'm going to switch to gas with indirect hot water eventually but I feel like it's too new to just junk. Also, I may move soon.

    Attachment not found.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Backup system for oil boiler - is this realistic?
    Interlude wrote: »
    I'd like to build just a small UPS-like system to run some LED lamps and . Figure about 40w worth of stuff, run about 4-5 hours per day. I'd need a battery, charger, and inverter (or a charger/inverter but are any of those reasonably priced?). Any recommendations for this kind of setup?

    Your first question was about powering everything (fridge, furnace, etc) during an outage... a system that large would be very expensive (compared to a generator) if only used a few hours a year. If you needed the system for 100's of hours per year, the generator would start looking like the more expensive option.

    Building a UPS system for a few lights for 4-5 hours per day can be a very cost effective solution if it means you are not running your generator for those 4-5 hours per day. Once again, the cost effectiveness depends on how often you need it. Is it worth spending a few hundred dollars to avoid using your generator XXX hours per year?

    Exactly what system I recommend depends on a few things... will there be an automatic transfer switch, or will you deploy it manually? The batteries we use in renewable energy (RE) applications are not usually the best choice for a UPS. UPS batteries spend most of their lives fully charged, waiting for the occasional call. RE batteries are being constantly cycled. You need to make a decision about batteries. From there, its fairly straightforward to pick an inverter and a charger.

    As for sizing the batteries, figure 40 watts X 5 hours = 200 wattHours per period of use, plus some for inverter losses... Call it 225 watthours. If you will be running your generator the other 20 hours per day (and charging the battery), then your battery will never be discharged more than 225 watthours. That's about 19 amphours at 12 volts. Therefore, a 50 ah battery at 12 volts would be a reasonable size. At that size for a system, you might want to consider a commercially made UPS system.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i