Solar Preheated Water and Oil Fired Boiler?

[Breakitnfixit]

Hello,

Currently have 20 yr old Trianco oil fired boiler running baseboard heat (closed loop?) and a DHW coil. Water from deep well runs 40-45 degrees year round.

The south facing 1800 sqf house is well insulated and I've only got a few more drafts to track down. Aside from adding insulated curtains/shades for the windows there isn't alot more I can do to keep the warm air in.

I thinking of adding evacuated tube (I'm in Vermont) solar collectors big enough to supply all DHW for the Summer and to supplement DHW in the winter as well as preheat inlet water to the boiler. I figure this could save 200 gal oil/yr just by keeping the boiler off in the summer.

Since the boiler is old and its chimney is falling apart (cinder block) I'm prepared to replace the whole system..

I'm thinking oil is still my best option (but I'm open to ideas here) and have some questions on configuration:

Should I keep it simple and pump closed loop solar heated solution through a heat exchanger in a well insulated hot water tank (120gal) and use water from this tank to supply the cold water inlet on the boiler (instead of from the well)? Additionally, the boiler could cool down the water from the baseboard loop by running it through an exchanger in this same tank? It seems like Buderus makes a boiler that would accomodate this set up.

Would this setup work (i.e. actually reduce oil consumption)? Am I right in thinking that 120 deg water from the tank could just 'flow through' the boiler for DHW without needing the boiler to come on? Would this also be preheating the water in the baseboard loop and is that ok? What are some considerations for routing the water? I'm trying to avoid lots of pumps and controllers.

My brain is starting to cramp trying to figure this out!

Thanks, CD

 

[BigLou]

Brekintnfixit,

Seeing as you are open to spending the money on a whole new system and oil is currently close to $4.00/gallon why not go for broke and do it right.
Oil is terrible, dirty, inefficient heat and in my opinion should be out lawed as a home heating option. The have condensing boilers but I am not sure you can buy one in this country yet.

I would suggest you get a High Efficiency gas(natural or propane) fired condensing boiler. I have one and love it. Its capable of 98% efficiency and it only produces the amount of heat I need between 84,000 BTU's and 20,000 BTU's depending on the out side temperature. No sense in buring enough gas to make 84,000 BTU's when all I need on a 40 degreee day is 20'000. It also vents and gets its make up air through a 3" pvc pipe so there will be no need to rebuild your chimney unless you want to install a wood stove.

Tankless coils are quite possibly the worse way to produce hot water. Seeing as you are installing a new system why not upgrade to a better hot water solution. I would go with your idea of a closed loop system with an insulated tank. The only change I would make is to get a tank with a back up heat source either a dual coil ( from boiler) or electric. Super stor has many options
http://www.htproducts.com/superstorsolar.html

To do this right and save money you are going to need several pumps there is just no way to avoid it. My boiler came with all the controls I need for DHW and heating The only controller you would need would be for the solar side, I know FWWebb is now selling complete systems so you might want to look there

here is a link to my boiler
http://www.buderus.net/OurProducts/GasFiredBoilers/GB142/tabid/92/Default.aspx

Good luck

Lou

 

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[Breakitnfixit]

Thanks for input, Lou

I did investigate condensing boilers early on but stopped when I found out a drain was needed for the condensate. This must remain a basement installation and there is not a drain down there. I'm not keen on adding a drain and pumping out the liquid isn't appealing either. Are there other solutions I'm missing? I'm definitely not married to the oil idea but the solar piece needs to stay.

Thanks

 

[BigLou]

breakitnfixit,

Why are you opposed to a condensate pump ? they are like $50 and the simplist part of the whole project to install, just plug in the pump and run some clear vinyl tubing and your done Its a small trade off for the 15%- 25% jump in efficiency (assuming you can operate in the condensing range)

We used 1350 gallons of oil a year with the old system it would have cost over $4000.00 this year. This past january my gas bill (biggest so far) was $135 for heat hot water and cooking, I just got my april bill for $56.00 I am expecting around $30 when the heat shuts off for the summer. If I had a solar back up it would be ZERO for the summer. So I am looking at about $1000 a year down from $4000

Where in VT are you ? is natural gas available to you ? Another option would be a indoor wood boiler with a large storage tank that could do dual duty with the solar.

Here are some pictures of my set up took during the instalation. It was not installed in an ideal location but you can see how we made due. I have a super stor but not a solar one ( it was here before I bought the house). If you look you can see the condensate pump and its drain line its really a non issue for the added benefit.
http://home-and-garden.webshots.com/album/561572191MXzZYj?vhost=home-and-garden
Lou

 

[Jadnashua]

Condensate needs to go to a drain, as pumping it outside in the winter can be a major problem. Most pumps have about 12' of head and a fair distance, so you could go up to the main floor of the house and drain it somewhere there. A washing machine stand pipe provides a fairly convenient location to drain it most of the time. If the pump fails, some have an interlock float switch that will shut things down if it fails before you get water everywhere.

 

[Breakitnfixit]

My first thoughts on pumping condensate were its another thing to provide power for, another hole in the house, another system to fail and protecting the water from freezing at -20 degrees. Since we have a septic system I'm not sure if I should add the extra load (a few gal/day?) but maybe that would be ok since the washer stand pipe isn't far away or is the acid content of the water bad for the septic?
We're very rural so natural gas isn't available. Going propane would require removing my oil tank from the basement and adding the propane tank somewhere (outside, right?). However, I have flirted with the idea of replacing the 20 yr old 275 gal tank with two new 330 gal tanks anyway since my location makes oil delivery in winter a real pain (like having to plow and sand just for the oil truck). I was kinda thinking if my system were efficient enough I could get through most of the winter with just the two tanks filled (I avg about 950 gal/yr).
I know I said I'm open to other plans, its just that I have put most of my thinking (hard work for me) into the oil route which I'm already familiar with. I suppose the cost would be roughly the same to go propnae given that I wouldn't have to do a new chimney (its pretty rotton looking from the outside anyway). I would also have to figure whether the condensing unit would always be running at max efficiency and what would I have to do to help it do so.
The scale is kind of even between both oil or propane but I'd need some sound advice to get me to commit to starting my thought process over to get comfortable with going propane.
Also, I haven't heard any negative comment on preheating the boiler inlet water with solar so either way I should get cracking on obtaining the needed hardware, right?

Thanks

 

[Breakitnfixit]

I should qualify my need for 'sound advice' to mean MORE sound advice. I'm not implying that any comments so far have not been helpfuL!. Thanks.

 

[BigLou]

Also, I haven't heard any negative comment on preheating the boiler inlet water with solar so either way I should get cracking on obtaining the needed hardware, right?

Thanks

If you go the tank route there is no need for the domestic hot water to pass through the boiler. There will be a two closed loop coils in the tank one for the solar and one for water from the boiler

The problem with using a solar tank to pre heat for a tankless coil is what to do with the extra heat from the boiler. It will work great when the solar tank is hot enough to not kick on the boiler but your boiler will over heat in the spring an the fall causing the pressure and temperature valve to open and blow hot scalding water all over the place.
IE all of the heat is absorbed when the inlet temp is 40 but in april when the solar tank is 80 the excess heat can't go in to the water with out over heating it . Those same BTU's will not go to waste in a tank where they can raise a greater volume of water a lower number of degrees

If you want to go the oil route go for it. I just always advise people to go the high efficiency route. A new properly sized oil fired boiler with a solar hot water tank will still save you a lot of money. I have also been told that some oil companies will give you a better price on "bulk" delivery of over 500 gallons

I hope you do get more comments here but most threads that involve design and sizing get very few replies here. There are some great plumbers on this site but I think the majority(both here and IRL) don't how to properly size and design a system or they just don't want to share the information. Cheap fuel and lazy people have made it ok for years to not do your home work and install the right sized system

What ever you end up doing make sure you properly size the boiler by doing a heat load calculation for the home, don't just get the same sizre you have or let some one tell you what size you need based on the square footage of your house

If you want help properly designing your system( what ever one you go with) including how many solar panels and where to locate them. feel free to post here or send me a PM and I will E Mail you

Lou

 

[Jadnashua]

The most efficient gas units use a condensing boiler, variable output, and an outside reset control. The Buderus unit I have is rated at 94.5% at full output, but as you modulate it down (it will fire at 20%), the efficiency increases as the same size heat exchanger can extract more heat when it isn't being fire at full power. The outside reset automatically adusts the boiler output temperature to match the load and to keep it running. Running it at 20% continuously is more efficient and more comfortable than running it at 100% 20% of the time. Once you've heated things up, and then things turn off, you waste a lot of that heat you paid for, but if you continuously produce just what you need, it is far more efficient.

A modulating unit gives you more leaway in having a correct heat load assessment, but still needs to be considered or you would not be running it at the lowest point where it is more efficent most of the time (i.e., if that low point is far more than you need most of the time, you've missd the mark).

I don't typically look at oil-fired stuff, so I do not know if they've been able to do modulating burners.

As to the condensate, if you were worried about the acidity of the water, all of the manufacturers make an add-on neutralizing kit. Basically, it runs it through a bed of minerals to raise the pH. You could run it to a new drywell if you didn't want to run it to your septic system.

 

[MikeP860]

CD, did you figure this out yet? I have a very similiar question posted in here. I have a relatively new oil burner with a tankless hot water system. I also have kids and every time they get in that shower, on goes the burner. I cringe at the sound and the fact that oil is still above $3 a gallon down her in CT. I also have circulating base board hot water heat. I also have 40-45 degree well water going in to the boiler. I built my own hot water solar collectors and I am very close to building the flow system indoors. I will be using a glycol based anti freeze mixture in my closed loop. I am running the hot solar water through a sidearm heat exchanger to the hot water holding tank. It's going to work...I tested it and I was giddy and smiling like I won the lottery for the last week. I need to know the same thing...if my oil fired burner pulls pre-heated solar water, versus near freezing well water, what are the consequences? Is there a better way?

 

[Ken Long]

I have a similar situation. I bought a house 3 years ago and it came with two hot water solar panels, a solar tank with electric back up and an oil furnace with a new tankless coil. I'm researching to find the best way to run the combination.
Originally, I turned the furnace off during the summer thinking I was saving oil but was told this would ruin my furnace due to condensation, it needed to stay warm and the better route was to turn the temperature for the tankless coil to low during the summer.
This seems to work well. During the solar season, spring through summer the furnace only comes on occasionally to stay warm, not when taking showers or doing laundry. During the winter heating season, I turn the electric backup off and turn up the temperature for the tankless coil as the furnace is generally hot.
I've never had problems of blowback from the furnace overheating the water.

The only problem I do get is too much pressure in the solar tank during the peak solar season and dripping from the pressure release valve. I replaced the expansion tank which remedied most of the dripping but I may need to add a second expansion tank. This problem is also easily remedied by turning the hot water on anywhere in the house to release the built-up pressure and is the worst if I run the cold water without releasing this pressure, such as flushing a toilet or watering the lawn.

 

[Reach4]

The only problem I do get is too much pressure in the solar tank during the peak solar season and dripping from the pressure release valve. I replaced the expansion tank which remedied most of the dripping but I may need to add a second expansion tank.

Second expansion tank, or bigger expansion tank.

 

[Dana]

Ken: In most the HVAC world "furnace" refers to a heating system that delivers heat via hot air in ducts, and is not the same thing as a "boiler". There are regional dialect differences on this, but using the terms interchangeably lacks clarity. Nobody would take the term "boiler" as a reference to a hot air furnace.

The notion that an oil boiler is ruined by condensation in summer isn't well founded. For condensation to occur a steady supply of air with a dew point higher than the boiler's temperature is required. A boiler in a cool basement might be below the dew point of the infiltration air into the basement, and stack-effect may be continually drawing some air though the boiler, but it has to be truly severe for actual damage to occur. Cold-firing an oil boiler not designed for it or chronically firing it at a temperature cooler than 140F will cause corrosive EXHAUST condensation on the heat exchanger plates (and in the flue), which is far more damaging than mere water condensation. If you have the boiler's summertime temperature set to 120F to prevent water condensation you may be doing more damage to it than simply turning it off. Sealing up all the air leaks into the basement and running a dehumidifier can pretty much prevent water condensation inside the boiler, as long as the hot water coil is being bypassed during those months. Cold water passing through an idling boiler's coil cools it off.

At the current price of oil, even at VT style electricity pricing it's cheaper to do most of your heating with a cold climate ductless mini-split heat pump, and use a heat pump water heater in the basement in summer (or even all year.) Even if the boiler is still necessary for the 99% design condition heat load, the much cheaper heat from the mini-split makes it worthwhile (and it provides high efficiency cooling in summer.)

A heat pump water heater does double-duty in summer, taking the latent heat of vaporization of the humidity in the air and converting it to sensible heat inside the tank. It's both a water heater and a dehumidifier, which also limits the condensation in the idling boiler. In winter it harvests the standby heat of the boiler room, putting it inside the tank, lowering the room temperature a degree or two. That lower room temperature also lowers the rate at which heat is leaving the basement via the foundation.