Mod-con Boilers and Outdoor Reset
I’m kind of thrown for a loop after speaking with a trusted heating pro I work with.
He stated that he doesn’t use outdoor reset on his boiler installs.
I have been under the impression for quite some time that installing mod-con boilers with outdoor reset in relatively low-load homes is the best strategy to achieve max comfort from a well-designed radiant distribution system.
Thoughts?
Comments
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Two thoughts:
- Fire your "trusted heating pro". Useless
- Your impression is accurate.
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Probably because he's not smart enough to know how to set it up.
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These responses are harsh. What kind of radiation is it? That matters significantly.
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there are some concern, it does tank longer to recover if you do a deep setback
On shops with a group if overhead doors that open and close frequently recovery can be slower If they are use to unit heaters blasting I have heard if boilers cycling more with the limited SWT
It us good for the owner to know how to make tweaks.
I think the ramp up feature on my Lochinvar will over-ride the ODR temperature, and the time of delay may be adjustable also?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Not installing ODR, even with a steep curve, is throwing money out the window. It also defeats the reason of the modcon as in most cases it won't be condensing.
A modcon without ODR will also be cycling way more so it will reduce the life of the unit.
ODR is your friend, make sure to set it up.
The other one is high delta T. Increasing delta T is free efficiency gain with no drawback (exception is long series loop), always adjust your pumps properly.
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ODR isn’t necessary in every situation. ODR helps when you have radiation paired with a heat loss that needs temps both above AND below condensing temps. Not every system has that. If you have infloor heating, congrats, you don’t need ODR. If you have hydronic air handlers, you may not need/want it either.
Second, you can get the same condensing without knowing the outdoor temp. You can set the supply to 110F, then if the thermostat isn’t satisfied, set it to ramp up in intervals. Basically accomplishing the same thing
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Hot_water_fan:
The radiation is usually a combination of under the subfloor “staple-up” aluminum panels (Wirsbo Joist Trak) and panel radiators.
The houses in question are often lower-load cases (with BTU requirements of less than 25 Btu/sq.ft.).0 -
@Hot_water_fan in floor radiant is the perfect pairing for outdoor reset and condensing boiler temperatures.
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@yellowdog infloor is perfect for condensing temps. But do you need ODR?
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You lose the "comfort factor" if you must wait a couple of hours for the mod-con to step itself up gradually to the point where the 'stat can be satisfied.
Additionally, a well designed mod-con with a tuned outdoor reset curve will be able to operate without a thermostat…………running continuously……………which is very much preferred over cycling.
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I am a firm believer in ODR. It provides cruise control to an otherwise on/off system. I try to use the lowest possible water temp too create near constant circulation in order to achieve the ultimate comfort and efficiency. Not using the ODR is like not using the boilers brain….ultimately a dumb boiler. Also, look at your equipment charts, the lower the boiler SWT the higher the efficiency.
Some may like that old hot rod experience of pedal to the metal gas…..break…..gas…break. Me I like cruise control just purring along like a kitten enjoying the ride.Jeffrey Campbell2 -
Additional thoughts on using ODR with under-floor radiant or in-wall radiant?
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ODR is fine in those applications! Go for it. The benefits are smaller though since you’re already in the condensing temps
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Less benefit on low temperature systems.
But we are in the comfort business, so the valve could be in consistent operation, constant circulation possibility.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream3 -
Most contractors I know that don't use ODR are just afraid of callbacks. Ideally a customer can adjust the setting themselves to fine tune it but many don't want to. Contractor has one instance where the curve doesn't satisfy the customers need and they may just not use it after that. I have a mix of baseboard and wall rads, I'm condensing through all of the shoulder seasons and down to about 20 degrees or so outdoor temp. I actually just watched it a bit over the last weekend when we had really cold temps and lowered the curve another 5 notches, so maybe even more condensing time.
The way I think about it is like this. If 180 supply temp is enough to satisfy the stat on the coldest day of the year then the supply temp can be lower than that every other day of the year. For infloor and underfloor systems, that already get lower supply temp, dialing it in further can provide more consistent and even floor temps, longer runtime for the equipment etc.
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I think most people would be surprised to find out how few days they are at design condition. Gathering a 20 year weather data takes just a few key strokes.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
@Hot_water_fan ODR is not necessary for any system, but for radiant floors, I think it helps more than any other system. My own system is 3 zones of slab radiant with a single zone of onyx staple-up underfloor. I am programmed to have it hit my underfloor radiant design temperature (140ish) at around 0° and then the logic controls the setpoint temperature above that. The temperature is based on what the staple-up needs and the 3 slab zones are piped thru a 4 way manual mixing valve which mixes those zones down automatically as the outdoor reset changes setpoint temps. When it is around 0°, the slab zones see about 110° into the zones. At temps below 20° or so, the boiler runs almost constantly unless there is a bunch of solar gain that day.
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@yellowdog it’s better for the staple up, but for slabs, wouldn’t setting it to 90F with a ramp up to 110F max get you everything ODR could? You’ll get long run times. You’ll get condensing. What’s missing?
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@Hot_water_fan call me ignorant, but how would the boiler ramp up from 90 to 110 without ODR?
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Many Modcons have settings that will start at temp x then add temp y every z minutes until the thermostat is satisfied. Call it indoor reset if you want. ODR is a fine idea. It’s not necessarily every install.
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Is the boost function available without ODR enabled on some brands? That would be a nice feature.
This is the Lochinvar Knight manual.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0
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