I'm getting more inquiries from folks with baseboard hot water heat that need relief from fuel oil or propane bills.
Has anyone experience with pre heating a storage tank to up the return water temps or other ways to employ geo with this type of delivery?
Is anybody aware of calculation software that will help asses the operating cost savings of geo assist for hot water baseboard?
In Michigan we tend to run our base board boilers at about 180 degrees.
Thanks for input.
Joe

Won't work.

Typical baseboard water goes out at 160-180 and comes back at 140 or so. It is mentally appealing to hope that a geo system could somehow supply most or all of that small required temperature differential for much lower cost given this year's reality of $3-4 propane and $4-5 oil.

Sadly, geo can't hack it. Geo's high performance derives from the fact that we don't need to be much warmer than adjacent ground temperature regardless of outdoor temperature extremes. Supplying 180 degree water to heat a room to 72 degrees is simply not what geo does.

Geo takes 40-60 ground temperature and makes 100 F or thereabouts water or air to make that 72 degree room temperature. The difference may sound minor but those few tens of degrees make a load of difference in how these systems operate.

Geo and baseboard simply aren't compatible.

Thanks for your thoughts Engineer.
I had hoped to hear from you.
You are correct that the typical operating temperatures are 180ish, but that is to achieveve 5-600 btu's/running foot. What about over-radiated homes or transitional weather? The btu/ft requirement would be lower.
Air to air heat pumps are not great in Michigan but do have value in fall and spring; what about 130-140 degree (making return water temperatures in reach of geo) radiation during transitional season, when btu/ft requirements are lower?
Joe

However......

I know a dealer in Colorado that does use his geo for baseboard heat to a certain point. He lets the HP heat the house until it's about 17 deg. outside. It's a 4 ton geo system, and it heats the house until it's colder than 17 outside. At that point, he switches to his boiler. Obviously, he doesn't get the full benefit of geo, but he lowers his bills this way.

Thanks Clark,
I spoke with a consumer today who spoke of a neighbor who may have a similar situaion.
I'm sure we all agree that it would work to a point, the trick would be sizing and projecting savings (might take more guts than I have to make those promises).
Just for fun, I have a customer with an oil fired steam boiler that wants relief too!
Who's got geo steam ideas?
Joe

You just need to drill REALLY deep. There's steam producing heat down there eventually..... :D

Even 130-140 is marginal for geo. Hard on compressor - head pressure very high and COP falls way off.

I wish I had an answer using geo - my mom in Mass burned 1000 gallons of oil last year running her 3 zone baseboard system, so she's looking at a $4-5k winter coming up .

My point is not to achieve 140 degrees with geo, but to operate radiation lower so that your condensate return is in the low hundreds. I don't have the numbers in front of me but you still get a large percentage of the btu/ft rating out of baseboard at 140. Your condensate return could then be elevated by the geo to 120 or 125 leaving the boiler to make up 15 degrees instead of 40, cutting fuel oil consumption.
The capacity deration could be handled with an outdoor temperature shut-off or perhaps larger diameter or more feet of baseboard. In floor radiant works at much lower temps obviously because of more feet. I'm not calling this perfect, just thinking out loud.
Ideal....no.
Plausible? Maybe.

Let's try it at your mom's engineer, let us know how it works out. lol
Joe

It is funny you mention running baseboards at a lower temp. Mom's house is 45 years old and she has replaced most of the windows, including 200-300 SF of formerly single pane sliders. That and she keeps thermostats at 60-62 all winter. That suggests to me that it is quite likely that she could run baseboard water at 140 or so. Her hot water is zone 4 into an indirect tank so the furnace stays hot all summer just for hot water. Last year I cut the hot water tank temp from 140 to 120, and this summer I reduced the high temperature cut-out on the furnace from 180 to 140.

Each summer she uses approx 90 gallons of oil just for hot water. Doing the math suggests that 90% of that heat goes to is off cycle standby loss - convection into the furnace room and up the flue. Switching to a storage electric water heater and shutting down the furnace all summer would probably pay for itself in the first year, but her oil heat guy whined at me about the risks of shutting down the furnace - condensate, seals, etc. Since I'm not there to service the thing year round I have to defer to him.

I'm quite tempted to leave the high temp cut out at 140 and see what happens this winter given all her new windows and frugal thermostat settings. Knocking 40 degrees off the furnace temp should help with the off cycle losses a good bit.

Getting back to your post I infer that you might be thinking that if 180 baseboard water comes back at 140, then 140 baseboard water would come back at 100 and be able to be raised to 125 by geo. I don't think that would happen - 140 degree baseboard water won't lose the same 40 degrees that 180 degree water does. It would go out at 140 and return at 115 or so. Geo could heat that to 130 or so at a COP around 2.0 or so. As you say plausible but not ideal.

Thinking out loud, to augment the geo output in cold weather I'd be tempted to use a tankless water heater controlled by thermostat Y2 to boost the water an extra 10-20 degrees rather than keeping an oil furnace with all its complexity and maintenance in service for just that circumstance.

At the moment, on a per Btu basis 15 cent electricity used resistively (COP = 1.0 ) compares quite favorably with $4-5 oil at 85% combustion efficiency, which is unprecedented in most markets. I'm not sure how long this situation will last. Electricity will likely rise in price.

I also wonder when and if someone will come out with a 2 stage heat pump able to make 180 degree water aimed at the baseboard market. By 2 stage I mean two separate compression cycles in series. Look at how bigger air compressors ( 7.5 HP and up 175 psig machines) work - air is compressed in a large cylinder, and then piped to a small cylinder and compressed further.

If I pushed Mom into a geo investment it'd probably involve yanking the baseboards and retrofitting geo with a Unico air system, thus avoiding all the baseboard hassle and providing AC for summer. Doubt it'll happen though - she's too cheap!

Thanks engineer for the continued input. I didn't expect my return water at 100 but 110 or 115 seems likely which permits you to do 1/2 your heating (if the target is 140) within geo parameters. My other thought for folks with unfinished basements is under floor radiant for the ground floor and forced units (like the toe kick or in floor units) for areas that can't be reached. Of course it wouldn't take long to pass the price of duct work.
Not sure why your mom's boiler guy wouldn't support less operating hours on the appliance, but lord knows you don't want to stick your nose in there, you'd be blamed for all future hic-ups in operation.
Joe

If the boiler is 80% eff., it needs to have 140 deg. water return or hotter. If you put lower return temps to it, you risk shocking/cracking the cast iron heat exchanger.

I see your up late your self tuff.
Depending on the boiler application your return can be about any temp if the system is designed well. In our area before the rage of using water heaters for in floor radiant, we used 80% or less boilers for floor and ceiling loops with the aquastat set at 125. I serviced a 25 year old Weil McClain this winter doing exactly that. Plugged chimney by the way.
I think we all agree that there is not much to be done for base board owners though, I threw it out there just in case something popped up that I hadn't heard of.
Joe

I would think that operating a boiler at lower temp decreases thermal shock. Worst shock occurs when a large zone that hasn't called for awhile comes on - several gallons of water at 70 (not 140, 100, 115 or whatever) hits the bottom of the boiler quite quickly. Then, almost as quickly, return water rises to its normal steady state value (110-140). Reducing the boiler's jacket temperature would seem to reduce, not increase, the delta-Ts and the associated shock potential.

The bigger issue, especially with oil, is that at colder temperatures the flue gases may condense and corrode the boiler. The condensate is very acidic and will eat up cast iron in no time. Condensing boilers have stainless heat exchangers to handle this.

Oil has far less hydrogen than either natural gas or propane so there should be less water vapor to condense out of flue gases. To my knowledge they haven't come out with condensing oil furnaces yet like they have with gas. Mom's boiler supposedly runs at 85% efficiency with flue gas around 400, so I don't think condensate is an issue whether at 140 or 180 jacket temperature.

If someone knows differently, let me know.

Thanks

Honestly folks if we could find a way to use geo with baseboard , we'd be way ahead of the game. Possible hazards to the boiler would be we easier to address.
Joe

I'm a little out of my depth here, but I don't think it's an issue with quantiity of condensate as much as the nature of it. I think it is generally sulfuric acid that forms form the relatively high sulfur content of #2 oil. I have seen pictures of nearly new cast iron boilers eaten away inside due to flue gasses condensing - it's not a pretty sight. The main causes are downfiring below spec and low water temps. There is a general rule of thumb that the flue temp needs to be over 400degF or so in the stack to avoid condensation in the boiler or chimney (brick chimneys are destroyed by this as well). There should be a manufacturer's spec for minimum water temp for your boiler. If you want to learn more from people who know far more than me, check out heatinghelp.com - lots of incredibly smart, experienced, and helpful heating pros there, mostly on the residential boiler/hydronics side. The topic of downfiring and condensation comes up from time to time so there's probably lots in the archives. Incidentally there are a handful of residential condensing oil boilers out there, I think Monitor makes one, not sure of the others. Definitely not mainstream, though.

I'll surf that link.

My Dad has a Monitor Kerosene burner in New Hampshire - loves it since it burns relatively little fuel

I'm a mechanical engineer with years of HVAC service experience before I decided to design.  I have to disagree with many things that "Engineer"  has to say.  I'm curious what type of engineer he is and what kind of HVAC experience he has. 
Reducing an iron boiler's return temp will cause condensation thus rusting out the heat exchanger.  If the boiler is over 85% efficient then it is a condensing boiler with a stainless steel heat exchanger and can handle low return temps.  But if this were the case then you should already have an outdoor reset lowering the supply temp.on warmer days.
Lowering the high limit on his mother's furnace will stress the heat exchanger causing it to crack and leak Carbon monoxide into her house.  This is why the service tech. recommended he didn't do it!
I'm not trying to be rude but I hate when people give bad information

Use of a three way mixing valve, or a primary secondary piping system will protect any cast boiler from shock cracking

This issue has ben adressed and tested with use of Zone temp, outdoor set backs , and modulating boilers . Most of time temps dont drop below 140 , but with tempering valves they could

As a side not I recently had the plesure to work on a 68 year old coal converted cold start ,gravity feed , steam boiler. talk about shock

I say gravity because it pulled off the bottom and top single pipe water first floor steam second