Leon82
Member
from what ive read usually
Replacement for 1960's era N.G. boiler....
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John Molyneux
Member
Everybody has their own preferences but if you read through many of the older posts here you'll find lots of recommendations for either a 'set it and forget it' strategy or relatively limited setbacks. Your 7* setback is pretty deep. So if you keep the boiler at a low fire it will take a while to recover, or if the boiler has to modulate to a much higher fire to catch up in a more reasonable timeframe you're not gaining that much net efficiency benefit because of the fuel you're wasting during recovery.
Also keep in mind that modcons only really start to become more efficient with return water temps around 130* and don't get into their optimal efficiency range until return water temps are well below that. Efficiency is also affected by whether the boiler is running a low fire vs high fire (lower is better). Here's a chart I like that shows this:
http://cd8ba0b44a15c10065fd-24461f3....vanillaforums.com/editor/1a/srzsvyuyyeqb.jpg
Also keep in mind that modcons only really start to become more efficient with return water temps around 130* and don't get into their optimal efficiency range until return water temps are well below that. Efficiency is also affected by whether the boiler is running a low fire vs high fire (lower is better). Here's a chart I like that shows this:
http://cd8ba0b44a15c10065fd-24461f3....vanillaforums.com/editor/1a/srzsvyuyyeqb.jpg
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^ thanks John,
That looks very much like the charts I've seen over the last couple of days.
I guess my lack of knowledge on the mod-con system shows!
I don't really understand the roll the outdoor reset plays in all this.
Does the installer set the max water output at say 150deg and the outdoor reset does it's best to keep the boiler at condensing temps?
What if the installer sets the max water output to 160deg? Would the boiler only use 160deg output when there's a big outdoor differential and step down to condensing range the rest of the time?
That looks very much like the charts I've seen over the last couple of days.
I guess my lack of knowledge on the mod-con system shows!
I don't really understand the roll the outdoor reset plays in all this.
Does the installer set the max water output at say 150deg and the outdoor reset does it's best to keep the boiler at condensing temps?
What if the installer sets the max water output to 160deg? Would the boiler only use 160deg output when there's a big outdoor differential and step down to condensing range the rest of the time?
Leon82
Member
With the Lochinvar you set the max temp.
Then there is a curve you set
One point is low outdoor temp
One point us high outdoor temp
So for example I have my low temp set at 7 my design temp and 140 degrees water temp.
The high temp is 68 deg and set to 110. I got a little more creative with my curve but this is a general idea.
There is also a temp you can set to block a heat call 70 deg default.
So if the installer doesn't come back to alter the curve you will need to. So you should work that into the price if you don't want to tweak it. This is an issue with a lot of the modcons I feel.
Then there is a curve you set
One point is low outdoor temp
One point us high outdoor temp
So for example I have my low temp set at 7 my design temp and 140 degrees water temp.
The high temp is 68 deg and set to 110. I got a little more creative with my curve but this is a general idea.
There is also a temp you can set to block a heat call 70 deg default.
So if the installer doesn't come back to alter the curve you will need to. So you should work that into the price if you don't want to tweak it. This is an issue with a lot of the modcons I feel.
Leon82
Member
No those are outlet temps. My max is 160 but it follows the curve to get there. It would probably be -30 before it got there.
In the recent cold spell with -10 I saw a max temp of 146 with it going to 156 because of the differential setting.
The most delta t I saw at the boiler with my own eyes was 22 degrees. Could have been more while I was sleeping
In the recent cold spell with -10 I saw a max temp of 146 with it going to 156 because of the differential setting.
The most delta t I saw at the boiler with my own eyes was 22 degrees. Could have been more while I was sleeping
^ interesting, thanks!
I could probably set my boiler nearly the same as the temps in NY and CT are pretty similar... but we only got down to -3 that cold Sunday morning.
My 99% outside design temp is +15F here, by my calculations at that temp to stay at 65deg in my house I need 27,000 BTU/Hr.
I have 141' of finned baseboard, at 120 return temp it looks like I'd put out 26,790 BTU's... so I guess I'm still in a good envelope?
I could probably set my boiler nearly the same as the temps in NY and CT are pretty similar... but we only got down to -3 that cold Sunday morning.
My 99% outside design temp is +15F here, by my calculations at that temp to stay at 65deg in my house I need 27,000 BTU/Hr.
I have 141' of finned baseboard, at 120 return temp it looks like I'd put out 26,790 BTU's... so I guess I'm still in a good envelope?
Leon82
Member
Even if your not condensing, your modulating. Its still better than an oversized unit
Leon82
Member
They should have an indoor temp sensor to work with the odr and get rid of the thermostat.
I think Bosch has just made something like this.
If I was an electronics guru I would make a gadget out of a raspberry pi with a temp sensor to send a voltage signal to the boiler as a cheap BMS system.
I think Bosch has just made something like this.
If I was an electronics guru I would make a gadget out of a raspberry pi with a temp sensor to send a voltage signal to the boiler as a cheap BMS system.
^ funny you mention the Pi... I have three of them- I use them as media players for my NAS... awesome little units.
I'll have to look at the install & user guides for the Lochinvar and read up on the settings.
The t-stats are Z-Wave units that I run off my automated home controller system. I can use them as simple temp sensors if the Lochinvar has programmable day & night setback adjustments.
I'll have to look at the install & user guides for the Lochinvar and read up on the settings.
The t-stats are Z-Wave units that I run off my automated home controller system. I can use them as simple temp sensors if the Lochinvar has programmable day & night setback adjustments.
Leon82
Member
Well it accepts 0 to 10 volt input for a few parameters
Google will get you some leads on manuals but supply house.com has them if you search there.
They don't have the khn listed yet though but the smart system should be similar
Google will get you some leads on manuals but supply house.com has them if you search there.
They don't have the khn listed yet though but the smart system should be similar
Leon82
Member
You set the time in the boiler and it handles the setback.
Thanks again Leon... you've really helped a lot!
Supplyhouse.com is where I got the quotation for the Lochinvar- the KHN's aren't stock units yet, but they'll get one for me if I order it.
I got my mini-split unit from them a few years back when they were known as Pex-supply... pretty decent to deal with, and they're local to me.
Supplyhouse.com is where I got the quotation for the Lochinvar- the KHN's aren't stock units yet, but they'll get one for me if I order it.
I got my mini-split unit from them a few years back when they were known as Pex-supply... pretty decent to deal with, and they're local to me.
Leon82
Member
Yea fastrack stuff get here next day.
John Molyneux
Member
"I don't really understand the roll the outdoor reset plays in all this.
Does the installer set the max water output at say 150deg and the outdoor reset does it's best to keep the boiler at condensing temps?"
No. The outdoor reset doesn't "try to keep the boiler at condensing temps" -- it just tells the boiler operate at a higher or lower output and that may or may not keep the boiler in it's condensing range. Your job is to set up a curve that lets the boiler run as efficiently as it can under a range of outdoor temps so that it's condensing as much as possible given your particular circumstances.
Think of it this way: There is a fairly linear relationship between how cold it is outside and how many BTUs are leaking out of your house. The colder it gets the more BTUs you need from your heating system to maintain a stable indoor temp and vice versus. So the outdoor reset is like cruise control on your car. You want to maintain an 'indoor temp' of 68 mph but the engine has to adjust based on whether you're going uphill or downhill. Like the cruise control, the outdoor reset curve tells the boiler to increase or decrease power.
Let's say on the coldest typical winter day (0*) your heat loss is 40,000 BTU/hr, and when it's 65* outside your heat loss is 1,500 BTU/hr. The outdoor reset curve simply tells the boiler what water temperature to send out to your radiators/baseboard at any given outside temperature between those two points.
Ideally you want to set the curve so that the boiler is sending out enough heat to just barely keep up with your heat loss. If you do that it will run fairly continuously, until something else makes the house warm up and trips off the t-stat. My curve is set based on 114* output under design conditions. If I drop it down to 110* it'll do OK during the day because of solar gain, etc. but it'll lose ground overnight and the house will be a couple degrees cold when I wake up. If I bump the design day end of the curve up to 120* or higher it will still be condensing but it will cycle a lot more. (You may need higher water temps depending on how much radiation you have relative to your heat load.)
My advice is don't worry too much about Delta-Ts or over-think return water temps. You have a given heat load and a given amount of installed radiation/convection (obviously you can and maybe should change either of these, but that's a different conversation). As long as you get your supply water temp as low as possible your return water temps will also be as low as possible. Once you get the curve close to optimal you can start messing with any other fine tuning capabilities your boiler may have.
Does the installer set the max water output at say 150deg and the outdoor reset does it's best to keep the boiler at condensing temps?"
No. The outdoor reset doesn't "try to keep the boiler at condensing temps" -- it just tells the boiler operate at a higher or lower output and that may or may not keep the boiler in it's condensing range. Your job is to set up a curve that lets the boiler run as efficiently as it can under a range of outdoor temps so that it's condensing as much as possible given your particular circumstances.
Think of it this way: There is a fairly linear relationship between how cold it is outside and how many BTUs are leaking out of your house. The colder it gets the more BTUs you need from your heating system to maintain a stable indoor temp and vice versus. So the outdoor reset is like cruise control on your car. You want to maintain an 'indoor temp' of 68 mph but the engine has to adjust based on whether you're going uphill or downhill. Like the cruise control, the outdoor reset curve tells the boiler to increase or decrease power.
Let's say on the coldest typical winter day (0*) your heat loss is 40,000 BTU/hr, and when it's 65* outside your heat loss is 1,500 BTU/hr. The outdoor reset curve simply tells the boiler what water temperature to send out to your radiators/baseboard at any given outside temperature between those two points.
Ideally you want to set the curve so that the boiler is sending out enough heat to just barely keep up with your heat loss. If you do that it will run fairly continuously, until something else makes the house warm up and trips off the t-stat. My curve is set based on 114* output under design conditions. If I drop it down to 110* it'll do OK during the day because of solar gain, etc. but it'll lose ground overnight and the house will be a couple degrees cold when I wake up. If I bump the design day end of the curve up to 120* or higher it will still be condensing but it will cycle a lot more. (You may need higher water temps depending on how much radiation you have relative to your heat load.)
My advice is don't worry too much about Delta-Ts or over-think return water temps. You have a given heat load and a given amount of installed radiation/convection (obviously you can and maybe should change either of these, but that's a different conversation). As long as you get your supply water temp as low as possible your return water temps will also be as low as possible. Once you get the curve close to optimal you can start messing with any other fine tuning capabilities your boiler may have.
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John Molyneux
Member
I'll be installing one in the next couple weeks and will report back. It just works with their line of boilers, however.
Thanks very much John!
I have a lot to learn about mod-con systems, but it fascinating to me.
A couple of takeaways then...
-No or minimal nighttime setback
-System will run fairly continuously
Both completely opposite of my current boiler.
My 99% outside design temp here is +15f, anyone have basic settings suggestions for me to compare against what the installer may setup?
Max output temp?
For curve setup:
Low outdoor temp?
High outdoor temp?
Thanks....
I have a lot to learn about mod-con systems, but it fascinating to me.
A couple of takeaways then...
-No or minimal nighttime setback
-System will run fairly continuously
Both completely opposite of my current boiler.
My 99% outside design temp here is +15f, anyone have basic settings suggestions for me to compare against what the installer may setup?
Max output temp?
For curve setup:
Low outdoor temp?
High outdoor temp?
Thanks....
Leon82
Member
Most days mine runs about 20 hours. It shuts off at about 6pm when me and my wife and kid are home and then starts when the house drops to 67.
You know your minimum temp is at 120 because of the shirt zone. You would divide your design temp btu by feet of baseboard. Then check the temp chart to see what temp it puts you at
You know your minimum temp is at 120 because of the shirt zone. You would divide your design temp btu by feet of baseboard. Then check the temp chart to see what temp it puts you at
Bear in mind, 120F output in Slantfin's documentation is average water temp (AWT), not boiler output temp, and somewhat optimistic when projecting output at AWT below 120F. Below that temp the output becomes increasingly non-linear, and is more affected by things such as dust-kittens, abutting furniture & drapes, etc.
Since you can meet the load at design temperature with an AWT of ~120F it'll always be in the condensing zone. The amount of additional benefit you'd get by finely tuning the outdoor reset curves are small, so don't try to get the last 0.5% of efficiency out of it with temperatures where output is unpredictable, (say, and AWT of 95F or something) which would likely lead to large room-to-room temperature differences, and you'll start short-cycling the boiler. With taller convectors or old school radiators you can go that low, but not with low-rise fin tube.
Since you can meet the load at design temperature with an AWT of ~120F it'll always be in the condensing zone. The amount of additional benefit you'd get by finely tuning the outdoor reset curves are small, so don't try to get the last 0.5% of efficiency out of it with temperatures where output is unpredictable, (say, and AWT of 95F or something) which would likely lead to large room-to-room temperature differences, and you'll start short-cycling the boiler. With taller convectors or old school radiators you can go that low, but not with low-rise fin tube.
