Partial Outdoor Reset Worth It?

D107

of which 4 are powered. Gain is 75K Btu. Zone 2, porch on slab only is 7.5KBTU loss (baseboard) with 25Kbtu gain.
Buderus G-115 with net ibr 64Kbtu (same as Peerless WBV) seems ideal for 47Kbtu loss. Porch rarely used so usually kept at 60deg. The proposal I have for the G-115 would put the main zone on outdoor reset, constant circulation and control DHW priority via the logamatic which would protect the boiler without primary/secondary. porch zone would be on existing thermostat. All achieved with 3 circulators.

Thanks,

David

D107

Peerless WBV, Prim/Sec with Tekmar Proposal

Apparently this setup allows supply water temps to get down only to 135-140 deg F probably for boiler's thermal protection. (Buderus G115 with logamatic I gather can go down to 104deg.) Problem is, assuming that 140 deg temp might be supply temp when outdoor temp is 25 deg or so, that leaves out savings at any outside temp above that, which would include alot of the shoulder season, unless I am misunderstanding something. (House is 47Kbtu loss and 100k btu emitters, monoflo.) Any way to pipe this to be able to use 100deg supply temp without fancy 3-way valves etc? We have decided to stay with natural draft with as high an efficiency as we can get. WBV seems pretty good, and it has the ease of service that is important.

I also hope that the upper supply temp limit could be 200 or so.

Tnanks,

David

Unknown

Use a boiler that isn't hurt by cold return water temps.

Otherwise, no, you can't avoid the need for mixing if you want cooler temps for the heating system, and you'll need that mixer to also do boiler protection for the boiler, so it can "balance" what its doing to avoid thermal shock or condensing the boiler while trying to keep the heating system happy.

CC.Rob

what kind of emitters?

I recall (perhaps imperfectly) a thread some months ago that the practical low supply temp for, say fin/tube baseboard, is around 140F. So lower end of supply temp might be in part a function of emitter type. Insight? Comment?

Unknown

You can run it cooler than that, but you need to be careful.

Modern Hydronic Heating by John Seigenthaler (available here at heatinghelp.com's store, in fact) has some good calculations you can use to size baseboard from various manufacturers for various water temp and flow rates.

Dan_15

I use the Buderus G215 which has internal mixing architecture that can handle low return temps down to 104*. Together with outdoor reset + Buderus indoor reset sensor, it is quite efficient even with 180* emitters that I have. Temp never reaches 180* even in the dead of winter. Max temp on the Buderus controller is 190*. The G215 may be rated above your load requirements.

Will_5

Many Good Choices

I would certainly look at using look at using a boiler with built in protection for an application with low return temps,for the small cost of the upgrade it is well worth it. I have been using the Burnham MPO's for a while now with excellent results.

Boilerpro_5

If I am reading right

You have only a 47K loss, but 100K of emitters (at what water temp?) If this is true,partial reset will probably be absolutely useless, because on the coldest day of the year, the supply temp may just get up to 140F. The rest of the year the system should be run cooler. I would seriously look for return temp protection for any typical boiler design because you will very likely be condensing in the boiler most of the winter due to low water temps because of the excessive radiation capacity.
BTW I have many convector systems on full reset, right down to 70F supply water, with no problems. Tekmar's literature talks about the response curves of different types of emmitters, with all being fully reset.
With the info you have given, a good condensing boiler will only be marginally more expensive than the combination you have given, if at all, and save quite a bit of fuel.


Boilerpro

D107

current water temp--on old boiler--180 only

it's an old hydrotherm/becket combo 25+ yrs old. This is for my mom's house and we wanted to keep it as simple as possible. I'm a little leery of the mod cons--longevity, problems with direct venting, in general seems like more things to go wrong. And maintenance is also an issue if the installer doesn't maintain it after the first year. Based on what I've gleaned from the wall, if the Buderus atmospherics can get down to 104 supply temps, that seems pretty good reset. Also the Buderus mod cons are quite a bit more costly than their atmospherics and even other mod cons like munchkin.

Thanks alot for your input.

David

Paul Pollets

Selecting what works...

Buderus makes a good boiler...the Logamatic control was designed specifically for the boiler. If you have a condensing load, which would be available if your heat emitters were oversized, a condensing boiler would be better suited. If only oil is available, the G115 with the Logamatic will be far easier to use. Yes, mod-cons, must be maintained. So do atmospherics. The greater efficiency will be there on a condensing load...Of course they cost more...there's more to the mod-cons. If you don't have a condensing load, no matter. I prefer the Riello burner package with the Buderus with an insulated chimney liner for best performance.

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D107

convectors provide less efficiency gain with modcons?

Thanks for your feedback Paul. I have heard that from reputable contractors--and if I recall correctly, convectors are #3 on list after radiant heating and cast iron rads in terms of mod con eligibility. I can't say if anyone's measured the percentages on this; I'd have to agree that such a setup would be better than atmospheric with outdoor reset; by how much I don't know. Of course Buderus mod cons are much higher priced than other well-reputed ones: Munchkin, NTI Trinity, Prestige, WM Ultra, Lochinvar's Knight.

David