Heating Help

too bad

@ January 3, 2012 3:39 PM in solar / radiant heat interface?

but not crippling. the 363 won't do "dump zone" control though, you'll need your solar controller to handle that.

use the high mass radiant curve for the radiant zones. Radiator will work fine as long as your design water temperatures are similar (my Rule of thumb is 20 degree spread per curve in design water temp requirements).

sure would have been simpler to do return reheat though ;)

Agree

@ January 3, 2012 9:28 AM in Buffer tank ,Mod Con, how to?

but with the same boiler firing logic determining when to fire, the apparent load on a boiler should not be any different with a buffer on the supply, or the return.

I don't believe you will ever get better efficiency out of an oversized boiler than a right sized boiler. By what I see with bin data (and I'm going to contradict the other post I made last night with the 50%-80% stuff, as I stopped looking at heating HOURS and starting looking at heating BTUs with my bin data):

1. Right sized boiler will be at under 20% modulation (min mod) for about 10-15% of heating BTUs per year.
2. Same boiler will be in the 20% to 50% range for about another 45% of heating BTUs.
3. and will be over 50% mod (where oversizing could help) for about 40% of heating BTUs.

If you double the boiler output, you are now:
1. in Cycletown (under 20%) for 45% of heating BTUS
2. at 50% or under for 55% of heating BTUS.

So you've only increased the percent of BTUs in the "sweet spot" by about 10% of total. But you've increased the percentage of your load that is cycling by about 30-35% of total.

That can't be great for the lifespan of the boiler, or for its efficiency, though post purge controls could help. and I dont' think going with a 50% oversize or anything like that yeilds much different results... your cycle period is going to increase faster than your "sweet spot" increase because cycle period BTUs occur at lower, more frequent loads and your sweet spot is extending into colder, less frequent hours.

have to be clear

@ January 3, 2012 8:58 AM in Buffer tank ,Mod Con, how to?

heat output = GPM x 500 x DT

If you cut flow in half and double the DT you haven't increased apparent heat output. To increase the DT without cutting the flow, you have to increase the load (pull the heat out faster). That means higher flow on the load circuit, not the boiler circuit, unless you are already under-pumped on the boiler circuit which is nearly impossible in most cases.

Increasing the FIRING DIFFERENTIAL, or Hysteresis setting on a boiler, will increase the firing time linearly. If it's set to fire to a 20 degree rise, changing that to a 40, with a 10 degree increase in supply water temp to make the average temp work out, would double your run times over what you are seeing now. That is helpful. In fact the advanced boiler controls with 'variable' boiler differentials will do that automatically in low load conditions to reduce boiler cycling.

but you can't increase output or reduce cycling by slowing down flow. Ever. In any circumstance. The only thing reducing flow can do is increase temperature rise which might be of value in some circumstances, but not this one.


If you have an oversized boiler, simply your options are only:

1. Zone Syncronization controls
2. Buffer Tank
3. Wider firing differentials (NOT loop Delta-T's)
4. Less, larger zones with higher flow rates and hopefully some mass like radiators or slab floors.


Wider Loop Delta-Ts might be better from a condensation standpoint and thus for efficiency: that's true, though I don't think most boiler manufacturers will allow you to run a 40 degree rise across their heat exchangers, most want you to stop at 30. But that will not help an oversize boiler with cycling control, it will only help with condensing efficiency. And Frankly, I am not even convinced it will help with that as I believe outgoing exhaust temps are related to the supply, not the return temps, but I am not a boiler engineer and I'm not sure which is most important for efficiency, return or supply temp.

why would you replace the pump

@ January 2, 2012 5:10 PM in Buffer tank ,Mod Con, how to?

wider firing differential would help... twice the difference is twice the firing length. but trying to achieve this with a slower pump just makes a short cycle worse. you have to get all the water in the circuit through the boiler fast enough to move the BTUs out.

slowing down the boiler circuit will not help achieve that. increasing flow in the secondary circuit would, if we do have a situation where we are heating the boiler, but not the rest of the circuit, too fast.

You don't get to cheat unless that boiler circuit has a... wait for it... buffer tank on it and the problem is already too little flow. but just changing the speed of water around a ring of pipe, without actually extracting those BTUs at a different rate, isn't going to change anything.

primary secondary

@ January 2, 2012 5:04 PM in Buffer tank ,Mod Con, how to?

is primary secondary. how much heat is extracted is about flow rates and temperatures, not how many different sets of closely spaced tees you are using. The best way to avoid hot water return is not to use primary/secondary... but then you better manage those flow rates well.

primary secondary

@ January 2, 2012 5:04 PM in Buffer tank ,Mod Con, how to?

DELETED. double post.

method 3

@ January 2, 2012 5:02 PM in Buffer tank ,Mod Con, how to?

is on the outlet of the boiler, which is the method I prefer.

then you can't satisfy your load until after the tank is heated.

heat in the bottom, out of the top as well... but that requires a sensor watching the outgoing water temps... then you don't initiate a demand until the tank is depleted. That typically requires external controls but some mod/cons have external sensing capabilities.

I disagree with scott on this

@ January 2, 2012 4:59 PM in Buffer tank ,Mod Con, how to?

the purpose of a buffer is to reduce cycling.

if the mod/con doesn't cycle when it sees the return water, then you don't need a buffer. this will occur with any system with a heat load over the min-modulation of the mod/con boiler.

But it only happens when you are over that load. the buffer tank is there for the 50%+ of the time that many systems are under the min-mods of the boilers on the system. If your min mod is more than 50% of your peak load, then you're in cycle-town for more than 80% of your heating hours.. close to 90%!

I agree that zone sync is a great alternative as well. but an oversize boiler will NEVER be more efficient than a right sized boiler. A right sized boiler is under 50% max fire for nearly all of the heating hours already, and you don't pick up that much going lower... whatever you gain would be lost with the problems of an oversized boiler.

the only difference is that with mod/con boilers you should be sizing by MINIMUM modulation as well as maximum. if your boiler has 4x the max output over another, but the same minimum (not that those exist, but still...)... then it's not "oversized".

HE

@ December 29, 2011 10:08 AM in Grundfos Alpha "fighting" a Honeywell SmartResponse?

is "heat exchanger".

we've done that too

@ December 28, 2011 10:02 AM in solar / radiant heat interface?

but in that case you can only use the solar if it satisfies the load (higher temp) and it's a much more expensive integration (363 is a very expensive controller).

Pay more, for less solar contribution... I don't see the additional benefit. I know the "it saves a boiler cycle" argument during the shoulder seasons, but my stance that anything that puts heat in the envelope saves boiler cycles over time, as it is heat loss over time that causes heat demands and then boiler demands.

not really

@ December 27, 2011 12:00 PM in Radiant Supply Panel Questions

just 15 years of low temperature radiant design experience and nearly zero air problems. Don't really care how fast the air leaves, as long as it doesn't restrict flow unduly, but usually we expect air to be gone within a few weeks.

bleed valves are not fun. we don't use any air valves other than the microbubble resorbers. which are very often on the return.

the difference

@ December 27, 2011 10:46 AM in Contender

is in energy usage, not first cost. also, it should be better for return temps too... bypass flow is much more controllable than primary, unrestricted flow of a pump in 10 feet of circular copper.

Also, you don't need a bypass if your smallest zone can pass the minimum flow of the boiler (typically min fire at a 20 degree dt but specs may vary by MFG). bypass is only necessary in small zone situations. completely not applicable in the single zone situation of the original poster.

In my mind

@ December 27, 2011 10:04 AM in solar / radiant heat interface?

there are only 2 ways to tie radiant and solar together that are worthwhile.

Simple: Delta-T control watches return water from radiant and tank coil temp. If return is colder than coil, divert with 3 way valve through coil (or inject with pump for high flow applications). Especially rocks if you're doing higher delta-t radiant or low temp radiant so return temps are close to room temp. will need a "boost heater" for DHW in that case as with any luck you'll pull that tank down to close to room temp most of the time.

More involved: Use the radiant as a "dump zone" with a high limit thermostat defining how hot you are willing to let the room go. that thermostat will open a zone/run the pump only when it is not too hot, and the delta-T control contact is closed indicating that the return return is cooler than the tank. This is nice, because when you have solar gain you might not have heat demands, so this allows you to dump heat into the house even if you are at "regular" room temp and 'charge' the house before allowing the tank temp to rise.

these are nice, fairly simple things to do. they also minimize tank temp which maximizes collection.

in any case

@ December 27, 2011 9:51 AM in Radiant Supply Panel Questions

the benefit of hotter water in the air eliminator is pretty small. with a good air eliminator you could put it anywhere it will see the air, and it would be fine.

also

@ December 27, 2011 9:48 AM in Contender

the presence or absence of an indirect has nothing to do with the need for primary/secondary piping. it's just a second primary loop (DHW pump is an either-or run vs the Boiler pump, assuming priority is used).

in a single zone system

@ December 27, 2011 9:46 AM in Contender

the only reason you would ever need primary/secondary piping is because of pressure drop through the heat exchanger.

New HTP diagrams are starting to show primary piped systems with pressure bypasses instead of primary/secondary... we've been doing that for years, of course, even though they weren't in the manuals.

it's not magic. If you have enough flow through a mod/con boiler to extract the heat, it will be happy. mod/cons don't have "thermal shock" issues. MFGs specify primary/secondary because most installers don't do math, not because it's really necessary in all situations.

the contender mC99 can pump 8 GPM through the boiler and lose 5 feet of head. If your primary pump contractor is prepared to calculate your flow requirements and frictional loss of your heating system, I would say he's a good bit smarter than the one doing primary/secondary on single zone systems.

couple things

@ December 27, 2011 9:40 AM in Grundfos Alpha "fighting" a Honeywell SmartResponse?

1. autoadapt sucks if you're doing any reset control. use a constant pressure mode on the alpha if you're doing a multizone system.

2. use a variable speed injection reset control from HE through the trench... turns the whole trench into an injection loop. large delta-T means you have one hotter leg and one colder leg, so you cut overall trench heat load and you can dramatically reduce the size of the pipes as well in most cases. also, you drop the need for a mixing valve.

reset control

@ December 27, 2011 8:38 AM in Buffer Tank Size

vs 120 fixed temp geo? you can easily add a an average of a COP for the season with reset. should be a 1 year payback or less on most systems, and it's not very complicated to add. if you can save an aquastat payback is exceedingly fast.

I will never understand why anyone spends the money on geo without reset. it's a small dollar add to really realize the efficiencies that geo promises.

again

@ December 26, 2011 10:41 AM in Buffer Tank Size

yes, with no load you are at 11 minutes. 21 minutes at design temp.

if you are really running 120, I hope you're using a reset control. waste of good geo efficiency 90% of the year to run at such a high temp.

unless you have a guaranteed load

@ December 22, 2011 8:49 PM in Buffer Tank Size

like a forced-time on air handler, use load equals zero for this calculation.

that is why your calcs are not matching expectation.

valuable feedback

@ December 21, 2011 1:54 PM in Just for fun, pumping backward

thank you sir!

not correct

@ December 21, 2011 12:43 PM in Buffer Tank Size

you do not use the heat loss: you have to buffer during part load conditions where loss could equal very nearly zero. You use the output of the unit at zero, or nearly zero load, unless you can be SURE of the attached load. for instance if you are attached for a forced air hydro system you know extraction will be X btu's/hr and if you had a minimum fan time you could be sure of that component of your runtime.