Controls on an oil boiler in Superinsulated house.

Ron Schroeder

Hi Wallies,

The house has R38 walls and R65 ceilings so the heating load is way smaller than the boiler's output. The boiler is a Buderus 115/21, the smallest available. Love the boiler but it can't help but short cycle with the tiny heat load. Outdoor reset wouldn't really help since the aquastat (L8124G) setting of 130 degrees is high enough even at zero degrees outside.

Indirect DHW on one pump and the 6 zones of baseboards on the other pump.

With the fixed 10 degree differential of the aquastat, the Riello BF-3 burner only runs about 130 seconds at a time (Not including pre and post purge).

Any ideas on controls options, buffer tank etc. for this system? Cost effectivnesss is a must since the low fuel usage would give a very long payback.

Thanks for any input.

Ron

Weezbo

Maybe....

Depends on the current nozzel size....in the F-3 other than that Good old IAQ can come to the aid...that is if the superinsulated home doesnt have an HRV...hrv's will improve the indoor air quality and throw maybe as much as 20 percent of the btu's right out the window ,which is hard to sell to an insulation happy individual..I know....i resemble that individual.

Joe@buderus

Control

Ron, I highly recommend the R2107 Control. My own home is very similiar to the house you discribe. My home has R37 in walls, R60 in ceiling, radiant in slab, 1645 square feet. Equipped with the G115/28 with R2107,BFU, M241 controling an injection valve,40 gal ST150 Tank. Use just under 500 gallons of oil per year.

The R2107 has miniumum burner firing temperature, condensate protection, large differential (especially during mild weather), DHW priority, warm weather shut down, etc... These features will insure a long service life of the equipment.

If you set the boiler aquastat at 130 degrees, DHW recovery would not be very good.

THIS IS A PERFECT APPLICATION FOR THE R2107 LOGAMATIC CONTROL. Consider constant circulation for even greater comfort and efficiency.

Ron Schroeder

Hi Weezbo,

The nozzle is a .5 Del 80W if I remember correctly. I have never seen anything smaller than that. BTW, it's a BF-3, not an F-3. The house already has an HRV with latent heat recovery with over 90% efficiency.

Ron Schroeder

Hi Joe,

The house is about 1200 sq. ft. and oil usage is less than the 275 gal. tank per year.

What would the R2107 do since the aquastat is already at about the lowest that the 115/21 should go without condensation. Would it increase the differential to give longer cycles. I don't think it could lower the boiler temp much since it is already so low.

The DHW tank is a LT-160. There is a second aquastat (4006X????)strapped on the supply line with a 180 degree limit that controls the boiler with a DHW call so the DHW recovery is phenominal. There is also a timer on the DHW circ to give the tank a post-purge from the boiler after the DHW aquastat opens.

Can I underfire the boiler any?

Ron

joel_19

Sizing

You won't be able to underfire it much at all because your at a .5 the smallest nozzel you can get is .35 and that's hard to find. Plus you'll probably be condensing in the boiler. I would consider making the boiler bigger via a buffer tank. There are a couple ways to do it but my initial thought would be a Superstore 60 or 80. Replace the tank aquastat with a simple Tekmar 256 to reset the house. then open up the boiler aquastat to 15-20 f should give a much longer run. Or use an aqua booster style tank piped right to the boiler to give it say 40 more gallons of boiler water capacity. Then pipe a 4 way off that with a motor for reset in the house.

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Ron Schroeder

Hi Joe,

Thanks for the info over the phone. It looks like a R2109 would have been the best choice when the boiler was installed 2 years ago, it looks like a slight reconfiguration of the exsisting controls will be more cost effective. I will probably rewire it with the low limit on the L8124G instead of the high limit as the main boiler control since the low limit can have the differential set at 25 degrees. I may also put in a buffer tank.

I will have to look into the r2107 and r2109 a little closer. I will probably use one of them in my next install.

Thanks,

Ron

Ron Schroeder

Hi Joel,

Joe@Buderus didn't reccomend under fireing the boiler. (even a .50 nozzle is hard enough to find ;-) )

I am thinking that I will just use the low limit side of the aquastat with it's differential set at maximum to control the boiler temp in the heating mode.

For a buffer tank, what do you think of plumbing the heating side primary/secondary using an electric water heater tank as a Low Loss Header? I would still keep the DHW on the primary side with it's own circ and 180 degree aquastat for boiler temperature control durring a DHW call.

After talking with Joe, we agreed that with the low load and over sized baseboards that outdoor reset wouldn't help. More differential and/or more mass is needed.

Ron

kevin coppinger_4

why a 8124?

a standard control is a 8148(cold start) vs tankless (8124)does it stay hot always...kpc

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Ron Schroeder

> a standard control is a 8148(cold start) vs

> tankless (8124)does it stay hot

> always...kpc

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 323&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_



I didn't do the origional installation so I don't know the reason that the L8124 was selected. Possably because of it's larger 24V transformer.

DaveGateway

Could the heating loads

be piped as a secondary loop off of the primary which would have the indirect, turning it into a buffer? If you pipe them after the return of the tank, the delta would increase greatly and give the boiler something to chew on for then 2 minutes. Hotest water would be available to the indirect first.

Ron Schroeder

I didn't do the origional installation so I don't know the reason that the L8124 was selected. Possably because of it's larger 24V transformer. The B terminal on the Low Limit is unpluged, so it is cold start.

Ron

Ron Schroeder

Joe B,

Are you saying pipe the Indirect in series on a primary loop? Wouldn't that cause the indirect to overheat if the boiler was hotter than the DHW and not really add much thermal mass if it wasn't?

Ron

Constantin

That's some super-insulated house...

... instead of approaching it from a controls POV, how about the inside-out indirect water heater idea that Siggy presented at ISH?

I.e. create a lot of buffer-mass in the system by using the main tank of the IDWH as a part of the primary loop. Then use the HX in the tank as a heating coil for domestic hot water. Presto, instant buffer that should significantly reduce short cycling.

Put a thermostatic valve on the HX coming out of the tank and you should be good to go. Considering you're using BB, the water should be hot enough... The only issue with most tanks is that the HX is in the wrong location for maximum heat transfer via the tank for domestic hot water. Ergomax, thermomax, etc. are notable exceptions to this rule of thumb.

Alternatively, you could simply add mass to this system by putting a electric water heater in the primary loop and leaving everything else as is. The only thing I'd consider is how to insulate the thing as most cheapo tanks are not insulated well. If the regular inlets and outlets are too restrictive, consider using the entry points of the electric elements.

Ron Schroeder

Hi Constantin,

I don't know if they will go for an expensive inside out HX since they allready have the indirect. I am more thinking of the electric HW tank as a buffer using the element openings for the primary side. I have several bolt on to NPT adapters that I could use. For insulation, I could box it in and blow the box full of insulation.

Ron

Blackoakbob

Joe B...

I like your train of thought, use the IDHW as a primary loop with constant circ and secondary loop the heating with a mixing valve providing a large volume of standby water without a concern of too low a temp for the HW or the boiler return. Best Regards,

kevin coppinger_4

8148

has a built in 20 degree diff....kpc

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DaveGateway

The only issue Ron

might be if the indirect only had a 3/4" boiler supply/ return. This system would probably never to see water temps over 160°, this would kill any bacteria in the indirect and would require an anti-scald mixing valve to keep HW down below 120°. Constant circ might not be the way to go as it would allow heat to migrate back to the boiler after it shut off. True, a reverse indirect with 1.25" piping and 20 gal of boiler water would be the best solution giving you buffering and DHW all in one unit.

Ron Schroeder_2

Hi Kevin,

That's good info to know. My manual only says the differential is non-adjustable but doesn't give the actual value.

Thanks

Ron

Ron Schroeder_2

Hi Joe B,

The indirect has 1" connections but as I mentioned above, I have bolt-on to NPT adapters that I could use with an electric tank as a buffer/Low Loss Header. They are 1 1/4" NPT.

Your right about the constant circ problem. Not the best solution for THIS system.

I was also thinking more about the buffer tank insulation last night and realized that since the basement is conditioned space, a little more loss down there would not be a problem. Like in my house, I removed some of the insulation on the baseboard piping to raise the basement temp. I also added more insulation to the near boiler piping...up to the flow checks and zone valves.....to reduce heat transfer into the basement in the summer. The DHW circuit doesn't need any more mass so the buffer tank can be outside of the DHW circuit and can cool down to ambient when it is not the heating season.

I think that the buffer tank should be seperate from the indirect to allow the boiler (not just the heating loop) to operate below the DHW temperature.

Thanks for the ideas and feedback,

Ron

hr

Some times

the buffer tank is the best fix when you have multiple small zones like yours.

HTP, the Munchkin folks, make a real nice 20 gallon buffer tank. It has four large taps for piping, as well as smaller connections for temperature wells, etc.

There are a bunch of different way to pipe in buffer, series,paralel, or as a P/S. P/S solves most problems IF you are not using a condensing boiler.

I have a few systems that I used electric water heaters as buffers. Get an energy saver model for the best insulation R value. Then I get 1" MIP X 1-1/4 copper to male adapters. this allows you to use the 1" element holes for connections. And increase to 1-1/4 " right there.

Again think out the controls so you can pull or push BTUs into and out of the buffer when needed WITHOUT going through the boiler. Else the boiler acts as a cooling tower

hot rod

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Ron Schroeder_2

Hi Hot Rod,

How much is the Munchkin buffer tank compared to an energy saver electric tank? I suspect that an electric tank would last about forever in a closed system. An electric tank would give you 2-1" or larger fittings at the element ports, a 3/4" port at the bottom (the old drain), a 3/4" port at the top (the T&P fitting), the two 3/4" input/output ports and possably even the anode port. That's a reasonable amount of ports. Unfortunatly, only two of them are 1" (maybe 3 with the anode port).

Thanks,

Ron

Ed_13

> ... instead of approaching it from a controls

> POV, how about the inside-out indirect water

> heater idea that Siggy presented at ISH?


This is a thermal store or heat bank. Look at this UK web site for an explanation. http://www.heatweb.com An existing tank can be converted using a plate heat exchnager, flow switch and pump quite eaily. The thermal store will prevent boiler cycling, by use of two cylinder thermostats, and also give DHW.

Big Idahoan

hot rod

do you have a simple drawing you could attach that would show the piping diagram, and controls.

joel_19

electric

Yep the electric tank would be cheaper. I don't know about lasting forever though. with the cost of the repiping work and all a few hundred more for stainless isn't a big deal to me. If it is to the H.O. then just give them the choice. I'd still make the rads WR it works so well , you can probably reset them much lower than the boiler aquastat is turned to now.

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hr

For the gallon capacity

that 20 gallon is a bit expensive. I would really like to see it offered in a 40 of 50 gallon capacity. 20 gallon pretty small for much buffer time. Blank insulated tank, no coil, 1-1/2" taps would be my request

Really the electric tanks work with that adapter. I can't imagine the pressure drop through a 3/4 or 1" X 1-1/4" adapter hurts much.

In this Viessman job the tank is the primary loop. The boiler and the loads closely tee off the 1-1/4" loop.

You could also do a p/s loop and treat the boiler, buffer and loads as secondaries. Costs you another pump however.

I'm not sure the anode couldn't be removed. Really don't need it in a closed system and really can't be in there if you are using glycol! Unless you use the AL friendly glycols available. A glass lined tank in a closed loop with the fluid controlled should last a long, long time. IMO.

Siggys buffer tank module on the HDS is very handy for "what if planning", by the way.

hot rod

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Ron Schroeder_2

Hi hot rod,

That's some purty nice looking plumbing. Looks like some if it is brazed. What program is that last picture a screen shot from?

One thing that I like to do (solar background talking here) is to use as few pumps and electric valves as possable to do the job to keep electric usage low. That's why I don't do P/S much.

Ron

Ron

Ron Schroeder_2

? joel

> Yep the electric tank would be cheaper. I don't

> know about lasting forever though. with the cost

> of the repiping work and all a few hundred more

> for stainless isn't a big deal to me. If it is to

> the H.O. then just give them the choice. I'd

> still make the rads WR it works so well , you can

> probably reset them much lower than the boiler

> aquastat is turned to now.

>

> _A


Hi Joel,

I'm having a brain fog here. Whats a WR?

Ron

DaveGateway

Bock storage tank

has a glass lined 30 gal with 4 2" supply/returns that wouldn't be as as cheap as a water heater, but you know you wouldn't see any pressure restrictions and probably cheaper then a Stainless steel tank.

hr

Ron

all the T-Drilled connections are silver soldered. actually I use JW Harris Blockade. a little more user friendly than silphos.

Check out Siggys program at www.hydronicpros.com. Should be a free demo download there. Used to be able to buy that program here at the bookstore?

Yeah, PS gets pump intansive. I think Laing pump has expanded their 12V DC pump selection if that helps any to run off your PV grid.

hot rod

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Ron Schroeder_2

Hi hot rod,

Thanks for the link to Siggy.

I have noticed some new pumps from Laing. I see that they dropped their one that drew only 2.9 watts.....less than most zone valves.

Ron

Ron Schroeder

Success.....this turned out to be easy

Well I sat down and stared at my drawings for a while and came up with an easy solution tha was even simpler than what was in place.

I plugged the wire back into the B terminal on the Low Limit so the boiler aquastat is now un-modified.

The IDHW aquastat is wired to the TV-T terminals on the L8124G but now also goes to the coil of a relay that is across T-Z so it pulls in at the same time as the relay in the L8124G. The N.O. contacts are wired in series between the B1 terminal and the burner. This makes the boiler cold start since those contacts break the connection to the burner when there is no call for heat and it goes up to the High Limit (180 deg) when the IDHW calls for heat. The DHW circ is connected to the C1 terminal so it doesn't come on until the Low Limit is satisfied (about 140 deg). I kept the timer to run the DHW circ. to purge the extra boiler heat into the IDHW tank.

Now for the heating. The end switches on the zone valves go to the T-T terminals on an 845 relay. The first set of contacts, 3-4 go from the B1 on the L8124G to the burner just like (and in parallel with) the contacts of the DHW relay. The second set of contacts, 5-6 on the 845 supply power to the heating circ. When the zone valves call for heat the burner comes on and the boiler comes up to the temperature controlled by the low limit which is set for a 25 degree differential. Now the burner run time is allways a little over 5 minutes.

Now if the house calls for heat and the IDHW calls for heat both circs run but the boiler goes up to the High Limit of 180 degrees. With the thermal mass of the IDHW tank, the boiler doesn't short cycle even with the 10 degree fixed differential of the High Limit. The boiler seems to have no problem with both loads at the same time but I could easily wire DHW priority wiring the spare N.C. contacts on the DHW relay in series with one of the T terminals on the 845 heating relay and the zone valve end switches.

I eliminated the strap on aquastat and a lot of wire and now it runs a lot better. The Low Limit is adjusted so the return temperature from the heating loop is 120 degrees with all zones on by the end of a call for heat.

Thanks for all the ideas and feedback.

Ron