Gales, Electricty and Stacking Functions

After a pretty good gale, we lost grid-power, so as I type this my generator is flying, and I am making my own power. It is good because the kids never even knew we were on backup power which kind of shows how untouched our lives are in terms of the power being out. But as things churn away, it got me to thinking…

I use a 20 KW PTO Generator driven by my tractor, but I got a few other engines that could power it. What would happen if I took the coolant flowing through my stand-alone engine powering a PTO generator, and diverted it into my radiant floor heat? As long as my main boiler loop is over 100 degrees, it will heat my radiant floor.

My question is, would a 35 HP engine produce enough BTU’s to heat my home? I think it might.

But then we get into another idea. Assuming the engine would heat my home, could an engine running 24/7 efficiently power my home? I know there is no way powering your own home would ever be more efficient then the grid’s cheap power, but would heating my home, along with powering it; tip the efficiency scale enough to make it worth it?

I spend about $2000 a year if I was to heat my home 100% through propane, and I spend about $2000 a year on electricity, so I would need to save $4000 running a generator to power/heat my home.

But here is where the water gets muddy. My Gen-Set does not care if my home is consuming 4 KW’s or 20 KW’s, it is going to produce 20 KW’s 24/7. That is way more power than what I need, so that extra power could go out on the grid. That is more money than I would consume in fuel by a long shot.

In reality, it would probably work something like this: from November to April I would operate my Gen-Set so that it powers my home, as well as heats it, and also send extra power onto the grid. From April until November I would probably just shut my Gen-Set down and take power off the grid because I would have a huge amount of power credits then..

I am trying to figure out why this would not work, and I am not coming up with a reason.

If nothing else, hooking the coolant system from the Gen-Set to my heating system would do two things. Even if all I did was run the engine during power outages, I would be heating my home for free while it was running. And alternatively, if running off from propane/wood/coal/geothermal while heating my home, the system would reverse flow so that my Gen-Set is always heated to 100-150 degrees making starting instantaneous.

I was doing some checking, and I got a few options for this.

I have a 35 HP Isuzu diesel engine that came off a tractor trailer refrigeration unit that would power my Gen-Set, but I also have a 6 cylinder diesel engine sitting in an engine stand. I was going to use it for a sawmill, so it is all set up on an engine stand, and even has a hand clutch bolted to it, but it was originally designed to operate a 30 KW gen-set. I thought it was bigger than it was, but it seems it is only 63 hp so it will not consume a lot of fuel.

My house takes about 450,000 btus to heat it per day, (5 gallons of propane at roughly 91,000 btu's per gallon), and assuming an engine consumes 10 gallons per day of fuel, it would kick off roughly 1.3 million btu's per day (10 gallons of fuel oil at 131,000 btu's per gallon), so even with some heat losses, there should be more than enough heat to heat my home.

I also checked my electric bill and it seems I use about 300 KW's per month, so I would only use half of the total KW's produced...

Travis Johnson wrote:I was doing some checking, and I got a few options for this.

I have a 35 HP Isuzu diesel engine that came off a tractor trailer refrigeration unit that would power my Gen-Set, but I also have a 6 cylinder diesel engine sitting in an engine stand. I was going to use it for a sawmill, so it is all set up on an engine stand, and even has a hand clutch bolted to it, but it was originally designed to operate a 30 KW gen-set. I thought it was bigger than it was, but it seems it is only 63 hp so it will not consume a lot of fuel.

My house takes about 450,000 btus to heat it per day, (5 gallons of propane at roughly 91,000 btu's per gallon), and assuming an engine consumes 10 gallons per day of fuel, it would kick off roughly 1.3 million btu's per day (10 gallons of fuel oil at 131,000 btu's per gallon), so even with some heat losses, there should be more than enough heat to heat my home.

I also checked my electric bill and it seems I use about 300 KW's per month, so I would only use half of the total KW's produced...

Travis numbers are great things! Assume that under perfect conditions you would be be putting out 33 percent of the energy of the fuel as exhaust heat, 33 percent as electricity and 33 percent as engine heat and noise. You would have to run your engine coolant through a plate heat exchanger so it does not contaminate the home loop and attach a heat exchanger to the exhaust to harvest that third of the power. Diesels have great compression ratios so they can take some back pressure from an exhaust exchanger. I think with economies of scale the utilities would still be "cheaper" but environmentally and efficiency wise you would win. Some utilities allow bio fuel net metering others limit it to solar and wind inputs. Personally I think you are better off running a genset at its ideal loading for shorter runs and charge a battery bank. A net metered setup would be best efficiency wise. an idling diesel will not produce nearly as much heat for exchanging as a loaded one so just running the house without either a battery or net metered arrangement will not harvest heat as well.  I usually use this reference chart for fuel energy content:    https://www.engineeringtoolbox.com/fossil-fuels-energy-content-d_1298.html

Cheers,  David

I am not sure if that is correct, at least the part about separating the boiler water from the engine coolant because they can be one and the same.

I do not use glycol in any of my systems because you lose 10% efficiency. So I could run straight water through the gen-set. In fact when I worked for the railroad, that is just what we did. Those locomotives have too much water in their cooling systems to run antifreeze...it is straight water, that is why locomotives run 24/7...especially in the winter...they would freeze if they did not.

Now a locomotive has a dump valve so when it hits 32 degrees, it dumps all the water just in case of freeze up. But you would not need this on a gen-set. That is because whether it was running or not, the main boiler loop would drop below 100 degrees, and the propane boiler would fire up to warm the water. That water would then be sent through the gen-set engine as well because it is part of the main boiler loop, so it would be 100-150 degrees all the time. That I why boilers can be placed outside even in unheated, uninsulated buildings.

But to do that, a homeowner must have back-up power because the circulators must push that warm water around. In this case it would not matter because the gen-set is the back-up power. The gen-set would also always start in any weather because its engine block is always 100-150 degrees.

We actually do this a lot in logging. We call them "spit swappers" and all it is, is a set of hoses off your pickup truck, that go to hoses on your skidder. You plug the quick connect couplers from truck to skidder and then as you enjoy coffee, the warm coolant from your truck, warms the skidder's engine. Then in 20 minutes, it is all warm, and it will fire right up. In that case the skidder and the truck must have the same antifreeze types, but it works really well.

But with a gen-set and boiler set up, the water would be just straight water.

I understand better now. I think I think plate exchangers because I've always incorporated domestic hot water.

David Baillie wrote:I understand better now. I think I think plate exchangers because I've always incorporated domestic hot water.

My wood boiler has a well where I can add a domestic water coil into the water jacket, but I have always had electric hot water heaters. I need to install a boilerMate and produce hot water another way, but I am not very motivated because my showers are always hot. My electric bill is not too high either, but it would be a lot less without an electric hot water heater humming...

It is just something I never prioritized...but should!