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Joined on August 20, 2009

Last Post on February 28, 2014

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@ December 10, 2012 12:56 PM in Bobcat boiler/Rad/Radiant System mixing valve issues

this is a complicated integration that really should be guided by a room by room heat load calculation and survey of your existing emitters. the following is NOT a substitute for actual math.

1. Slab could need anywhere from 80 to 140 depending on floor coverings and heat loads. usually it needs around 100 degrees.

2. joist could need anywhere from 90 to 160 degrees depending on floor coverings and heat loads. but it usually needs around 120-130.

3. radiators could need anywhere from 110-180. in existing homes it typically needs 140-160 unless very serious insulation upgrades have occurred.

4. kickspace heaters need a bare minimum of 110 and usually ship with an aquastat that requires 120 minimum or they just won't turn on.

also, your joist heat should really be insulated with real insulation, not just foil. If it's just foil, then you'll probably want even more water temp.

so you could be in any of the following situations:

- all emitters could comfortably run on one reset water temp, except the kickspace heater.
- your existing emitters may be appropriately assigned to mixed/unmixed, except the kickspace heater.
- Your joist radiant might be better suited to the unmixed temp
- Your joist radiant might be too high for the slab AND too low for your existing radiators to run properly.

problems that would indicate you need to do additional thinking here, once you've set up your outdoor reset and moved your high temp returns to the boiler side of the mixing valve cold leg:

A: radiator areas don't keep up or dont have even comfort through the rooms.
B: joist areas don't keep up, or have short demand periods of warm floors with long periods of cold floors in between.
C: Slab areas have "flywheel" problems with temperatures rising too much after heat demands.
D: kickspace doesn't run. honestly I hate those heaters... try to find something else to do there. otherwise, maybe you can run it off of your indirect water heater or something else that gives you fixed temp rather than ruining your reset curve.

How far apart

@ December 10, 2012 12:25 PM in Bobcat boiler/Rad/Radiant System mixing valve issues

are your water temp requirements for your high temp and low temp circuits?

If you don't know, what kind of radiant are we talking about for the mixed zones?


@ December 7, 2012 2:51 PM in Grundfos vs Wilo

yes, I'm not sure exactly what set point is supposed to be for unless you're using the pump as an injection mixing device.but it certainly is not a constant pressure mode, and not helpful on any system using reset water temperatures... as they all should be ;)


@ December 7, 2012 1:12 PM in Grundfos vs Wilo

that's fixed speed, not constant pressure. If I run at a fixed speed, it doesn't change speed based on pressure (i.e., how many zones I have open). Fixed speed is how all normal non-modulating circulators operate.

the delta-T operation in a residential circ is nice. but for me to use it I have to nearly double my total system flow rates which would both strongly reduce the benefit of using ECM in the first place, and would also increase the number of pumps I need on most systems.

the algorithm

@ December 7, 2012 11:00 AM in Grundfos vs Wilo

is posted lower in this thread: max head at max flow, half head at zero flow, line between the two.

I just went around with my local wilo rep trying to figure out why the heck I would want to cut my HEAD in half just because I had zones closing... I design for a given head in each zone, and I need the same head in each zone whether other zones are open or not.

However, in applications where your COMMON PIPING is a significant proportion of your head loss (mixing valves, heat exchangers, small common pipes, large zone counts with lots and lots of flow maybe) then as zones close the head in the common piping drops and you don't need as much.

so this is how I would use these pumps:

1. If you have significant losses in piping that is common to more than one zone, use the "variable pressure" mode on WILO

2. If you do not, and have multiple zones, with reset water temps/long on times, use constant pressure modes on WILO or Grundfos

3. If you have multiple zones with fixed water temps, then AutoAdapt on the grundfos can be ok. I'm not convinced it's necessary though and would probably choose constant pressure still for predictability.

4. For single zone systems, or systems where you are designing for the SAME delta-t in all your zones, then Delta-T based operation is great. might be Bumblee time in that case.

I can't believe Taco is releasing the bumblebee without a constant pressure mode. I am really bummed about that. I guess they are assuming that everyone designs for a constant delta-T in all their zones, which is really unfortunate. I'll definitely look at and use it for delta-T apps that aren't large enough to need Stratos sized outputs, and I have some, but man. they could have nabbed it all if they had constant pressure instead of fixed speed as the fallback setting. ah well.


@ December 7, 2012 10:43 AM in Bobcat boiler/Rad/Radiant System mixing valve issues

is that returns 1 and 2 are on the mixing valve circuit. so their returns, which are presumably too hot for the mix circuit, are able to hit the mixing valve cold leg. not good. if you fix the mix header piping by cutting the loop, you'll probably start to see yourself pulling water that is way too hot whenever your high temp zones are calling.

Ironman is right as well, you definitely want to run this boiler with reset.

another option

@ December 6, 2012 10:44 AM in Hello everyone . Just a few questions regarding radiant heat

if you want to economize and don't mind looking at a few radiators is a plateless radiant system with panel radiator supplemental.

the supplemental is usually small, and you can get conditioned floors and low temperatures more economically than with extruded plate systems. but, there is aesthetic issues and furniture placement issues to consider.

I do not recommend

@ December 6, 2012 10:42 AM in Best Pex Tubing

rubber be used in heating systems. no onix. We've seen degradation in some systems.

PEX, PAP, or PERT are all good choices. In most cases you want to be sure you're using something with an oxygen barrier. specific pipe selection depends on what your application is.

there are no self-sealing pipes out there.


@ November 29, 2012 10:00 AM in Slab temp rise

no need for a flow switch. single zone system, on is on. if it's zone valved, you need to be more careful.

this water heater is definitely below 30kBTU/hr output... not many 88% efficiency water heaters for space heat out there. but let's be super nice and say it gets 30kBTU/hr. If you have a 4" slab, it would heat a 35x35 slab 1 degree F every 20 minutes if we can dump the full output of the water heater, which we should be able to do with this loop field. WITH NO HEAT LOAD AND WITH A DRY SLAB. if this is a fresh slab, initial startups can take extra long.

BUT, you have to deduct the heat load. you say design load is 37kBTU, basically, and you are basically at an average of half load. so now you only have about 12kBTU/hr left on your generous 30k output water heater. Now you're more like 1 deg F per HOUR of runtime. from 40 to 70 would take about 30 hours. and that's just slab temp... if you are starting with a room temp slab, that means you are picking up 1 BTUs/sq ft of output to the room per two hours of runtime, and until your output hits your heat loss, you're short.

not exactly accurate: load is lower when the room is colder, so actual performance could be a bit faster. also, this doesn't account for the heat absorption of the dirt in contact with the slab if the edges aren't insulated. It presumes your load is correct. and it presumes that the slab is dry, again.

but it should illustrate that there is no fast response here.

If you want to juice up recovery with output, don't bother putting in a heat source sized for more than 30 to 40 BTUs/linear foot of pipe in this case. that's probably about the max emission you'll get. maybe slightly more. I am making that number up though as a ballpark aid.

really though if you want fast recovery you don't want slab radiant....

they are both good

@ November 28, 2012 3:37 PM in Boilers: Electro vs. Thermolec

but we are very impressed with the robust construction of the electro and have adopted it.

both units could stand to learn a bit about how to set up an ODR function too... I find both of them restrictive and silly. but better than nothing.

the industry standard

@ November 14, 2012 2:05 PM in wood boiler safety

is a generously sized pipe, piped such that flow can exit the boiler without power (directly up from the boiler, gravity recirc), to a bank of fin tube convectors sized for 15% of the boiler's rating. it should be sloped down to assist the circulation.

I don't know if this works with the greenwood, per se, and you should check with them. checking their website I don't think they even do this style boiler anymore, do they? the frontier they sell now appears to be a different design.

to clarify

@ October 11, 2012 10:25 AM in staple up w plates insulation opitions

only one type of plate wants convection, it's called "ultra fin". there are light plates that are conductive that are the vast majority of light plate joist installs. no airspace needed there.


@ October 10, 2012 1:50 PM in Piping radiant heat mixing valve

what temp is the valve set for?

can't tell what your piping is doing. supply water (hot) should be on hot side, your mixed circuit return water should be cold side, and you should be pumping out of your mix outlet to the mix supply side.

if you are doing that you should never exceed the temp setting on the valve. you are getting near max temp so either you have it piped wrong or you have the setting at max.

if you have plates

@ October 10, 2012 12:27 PM in staple up w plates insulation opitions

you don't need an airspace. difference is minimal in the extreme.


@ August 27, 2012 10:42 AM in To chill or Not to Chill, That is my question

insulate the back side of a radiant panel, no matter what. otherwise you have an uncontrolled emitter. hard to get desired comfort that way.

we have

@ August 27, 2012 10:30 AM in To chill or Not to Chill, That is my question

floor and ceiling and I have to say, it doesn't seem to impact output much. probably because the floor is purely a radiant addition and it's facing an already cold surface, the ceiling. Walls would probably be better because they are perpendicular to the ceiling.

ALL TUBING will need plates if you're doing drywall. you want as close to complete aluminum coverage as possible. walls or ceiling. no loose pipe.

the RPA

@ August 27, 2012 10:19 AM in water heater for radiant heat source?

changed hands and they let the old site go down, unfortunately. Lot of collected wisdom just poof! such is life in the cloud.

a water heater would probably do well in apartments. your heat loads are probably very small. but math should be done to verify.

a single heat source has advantage but little payback in these circumstances. better than 4 boilers though for sure.

in general

@ August 27, 2012 10:14 AM in To chill or Not to Chill, That is my question

if you need much more than 20 BTU/sq ft of cooling from a ceiling, you need supplemental. That's a physical limitation in most cases unless you are in a super arid climate.

might need to add some wall if you can't do air backup.

I may be mistaken

@ August 24, 2012 9:31 AM in Myson Low Line Convector

but I think they are only adjustable down to 110 deg f. not so good for a radiant reset curve unless, again, you can take the tinker route and use your reset water temperature curve as a proxy for when you'll need stage two help. that's unlikely to be perfect but it is cheap.

if you are using a stage 2 thermostat though, and can keep up until you need water temps that high, you're golden.

I hear you.

@ August 23, 2012 8:01 PM in Chilled ceiling design

the best I have for you until someone smarter than I chimes in is "be conservative". that's why I would generally use a high output panel... to ensure I can get that surface temp as close to water temp as possible.

we can do this kind of design but it's still bleeding edge for sure. not a mature process and some information, such as you request, as far as I know simply doesn't yet exist.


@ August 23, 2012 7:16 PM in Chilled ceiling design

good luck on that one. best I've gotten is 1.9 BTU/sq ft per degree difference ceiling surface to room, assuming flat ceiling in typical rad ceiling height ranges.

I would recommend a high output panel like warmboard-R or Roth panel to be sure not to come up short in most cases. If you find anything better though please do share.

I think it would be easier with preinsulated lines...

@ August 23, 2012 4:01 PM in What kind of pipe?

but sizes for preinsulated pipe are pretty limited. may not be possible to get what you need.

I am generally specifying hard pipe to allow the insulation to be done properly, but maybe a PEX-AL-PEX if you are tooled up with good fittings would be a happy medium.
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