Heating Help

good question

@ September 28, 2011 3:25 PM in control for intermittent input into radiant slab

"homeowner's ultimate goal" - don't know that there's a single bottom line. comfort. low-cost. eco-friendly. easy. the usual mixed bag.

I just laid out all my concerns to them with this electric approach and we're going to meet to reassess in the next day or 2. will see if they want to continue on towards an electric boiler with some known issues (of unpredictable magnitude!) due to the off-peak interruptions & resulting complex control mechanisms. or flip over to an LP unit which they started out preferring not to use.

one rub is that I pretty much steered them down this path based on my personal experiences with our other local electric utility - where their "off-peak" program is interrupted for only 5 hours at a time and slabs seems to be able to coast through that no problem. didn't have experience with this other utility's program but assumed (wrongly as it turns out) that it would work fine with slabs, too. big oops.

but at least I'm being straight with them about the issues I have come to see & they are good clients and appreciate that.

I will draw this out at some point. solar tank is a 2-tank system, with space heat being drawn off the first larger domestic preheat tank, and solar input being directed to 2nd tank as a priority and when that's satisfied, back to the preheat tank which can contribute to the space heat side. I'm pretty comfortable with that setup and controlling it - have done it on other installations & it works fine.

well, I'm an advocate for simplicity when possible, but got myself into some complications here and at least I see I'll benefit by learning some about injection-mixing, Tekmar controls, etc.

thanks for your time & comments, Steve. I'm not done with this one by any means, but it sure is nice to be able to come here and know that lots of people are kind enough to have my back ...

Roy

thanks guys

@ September 28, 2011 12:04 AM in control for intermittent input into radiant slab

Steve - yeah, plan is for a 120 gal tank as a solar preheat for the domestic hot water, and I plan to be able to pull space heat off that tank. solar will go to domestic water heater first and then to 120 gallon tank when water heater is satisfied. if I can figure out how to control things, I think I could electrically top up that tank at night, then draw it down into the heating system before the solar would get around to wanting to heat the tank. devils in the details on that one, and I don't have them worked through yet ... ;-)

cattledog - many thanks for your thoughts. I am not really up to speed on injection mixing and will need to change that to fully understand your concept here, I think. perhaps Tekmar might help me with that - or I'll give Siggy's book a try.

is the idea with the Tekmar that as the slab sensor approaches the target temp, it reduces the temp of the supply to the slab and thus minimizes overshoot? that makes sense conceptually, and would seem to be even better if the response curve can be customized to address this situation with extended "outages".

can outdoor reset then adjust the target slab temp? - it seems like that would be desirable if its a straightforward thing to do.

your other suggestion as I understand it is with a thermostat with a tight differential, like the HeatLink. I like the simplicity compared to injection mixing (as best I understand it) but my gut sense is it wouldn't do that well at avoiding overshoots.

am I am more or less understanding your ideas?

control for intermittent input into radiant slab

@ September 26, 2011 2:15 PM in control for intermittent input into radiant slab

OK, here's one that I'm scratching my head on.

radiant slab heating system plus a wood stove for quicker response heating. cold climate.

slab to be heated with electric boiler and with solar combi-system doing DHW & some space heat (160 sf collectors - won't get real deep into space heat load but should contribute a fair bit during spring & fall).

homeowners prefer to go with off-peak electric rather than propane for heat. utility program offers half-price off-peak electricity 12 hours on weekdays (8 pm to 8 am) and full time weekends, and any electricity used daytime on weekdays is double-price. owners both work days so this jives pretty well with their schedules. the plan is to try to use electric heat for slab only during 8pm to 8am period, put any solar input in during day, use woodstove to bump up temperature more rapidly when owners come home from work.

in real cold weather, if needed, the off-peak control can be overridden manually and some of the high-price electricity used to even out the heat input.

homeowners and I are aware that there will be temperature fluctuations in this setup - more so as the outdoor temp drops, and they feel this is the way they want to go. unfortunately I really don't know how to model a heating system with these sorts of non-standard inputs, so its hard to predict how it will perform.

my main question at this point is how to best control the electric input to the floor when we are running the electric boiler only 12 hours a day. I understand that high-mass systems are best at stable target temps - and I have had no problems controlling them when heat source was always available. but with no electric heat for 12 hours, indoor temp will likely drop some, and then overshoot.

my hope is to figure out how to dampen that oscillation without getting too complicated. I wondered about using some sort of outdoor reset, where the supply temp from the boiler corresponds to outdoor temps. fine tune that curve from experience over time and I'd think that would help a lot.

thoughts on this one??? I know this design raises a number of issues - including the perspective that its not a good overall approach … at this point I hope to focus on ways this approach could be optimized, rather than going a whole other route, like an LP boiler.

Roy

not exactly, as far as I know ...

@ August 15, 2011 9:41 PM in Outdoor pipe wrap

current WI requirement: "Exterior insulation must be covered with jacketing capable of withstanding moisture, ultraviolet radiation, and environmental exposure."

my guess is Aerocel would say their insulation is capable of withstanding this stuff without jacketing. not sure how the state folks would respond to that and the whole program is being reviewed (our current state gov't a bit less renewable friendly than previously) so who knows what's down the pike ...

Aerocel?

@ August 6, 2011 9:47 AM in Outdoor pipe wrap

is one of the closed-cell elastomeric type insulations, but unlike others I'm aware of (Armaflex, K-flex) it is EPDM based. manufacturer (AeroflexUSA) says it will handle UV and can be installed outside without jacketing or painting.

from what I can find out, the product hasn't been out there long enough to give real-life testing credibility to that claim, but the fact that EPDM is widely used as a sheet roofing leaves me thinking it may be legit

I've used Aerocel recently for solar installs because it has a high enough temp rating that it meets WI's state requirement for solar pipe insulation (250° F) - with Armaflex you have to go to their high-temp line to meet that requirement and the the price on Aerocel is considerably less than Armaflex HT. to date I've been jacketing Aerocel with the white PVC but I can't say that I feel great about the PVC - even in white - over long-term UV exposure.

I've got a project now to replace pipe insulation on a system that originally had fiberglass & brown PVC on its external piping. the PVC failed early on - warped, buckled, and faded. my plan was to pull off the fiberglass, replace with Aerocel, and then do aluminum jacketing (the collectors have mill-finish frames so the aluminum would at least match that). a call to my insulation supplier led me to reconsider that (price/availability of aluminum) and they suggested the Aerocel unjacketed.

so I'm thinking unjacketed Aerocel might be a legit exterior option and, in a "time-will-tell" situation like this, I'd sure prefer to have more than manufacturer/distributor promotion to go on. EPDM as roofing is encouraging.

any thoughts/opinions/experience with Aerocel unjacketed?

similar issue

@ June 30, 2011 4:42 PM in Mixing valve malfunction?

I ended up having Honeywell send me 100-145° replacement cores for 24 AM1 mixers to replace the original 80-120° cores. no way that I could get them to put out consistent 120° water with the original cores - more like 115° and that was not acceptable to me or the client.

just returned all my honeywells to supplier and will try caleffi now. slightly pricier but if they work I will be a happy convert.


hr - what's the diff between the caleffi 521 series and the 252 series (solar line) besides the color of the knob? the specs look pretty much the same at first glance.

not a lot of room

@ June 25, 2011 9:01 PM in groundsource heat-dump solar trickle-charger?!?

beyond what I already have, which is a 120 gallon tank which feeds a 50 gallon electric water heater with the elements on switches. 50 gallon tank is priority for the solar energy, when its satisfied the 120 gallon tank gets heated. with only 96 sf of collectors it seems like this would be enough storage.

thanks for the thought, though, Bob.

one more ...

@ June 23, 2011 2:09 PM in groundsource heat-dump solar trickle-charger?!?

any suggestion (Mark or anyone) on reliable, cost-effective ground temp monitoring gear?

I put the temp sensors for 3 of these:

http://digitalthermometers.net/browseproducts/Digital-Aquarium-Thermometer-AQ150.HTML

down CPVC tubes into a sand bed once. as far as I know they are still working after several years, but they seemed a little lightweight in construction. @ about $20/sensor the price seemed about as good as I was likely to do.

anyone fond of another device?

thanks ...

@ June 14, 2011 1:36 PM in groundsource heat-dump solar trickle-charger?!?

for thoughts here from all. was just going to reply to Karl (hi Karl! see you this weekend at the energy fair, no doubt, and yes I''ll be around over the 4th. hope your place is coming along ...) and say that I am imagining drilling rather than driving the heat exchanger(s) into the ground.

and then I see your post, Mark, which looks significantly like you've tried pretty much the same concept I have in mind. I have a drainback system, so stagnation & heat dump not the issue. and my soil is pretty much pure clay. it can be wet, but not really much, if any water flows through it due to its monolithic density. I'd love to get a better sense of how heat would behave in this - would the rate of conduction just pull it all away and pretty much equalize, as Rob suggests, or is it possible that some sort of thermal bubble would build up? some sort of temp gradient would result, I'm sure, but no idea how steep it would be. and I have to say that all the various college math courses that would help me think about this appear to be long gone from my head (like heat into clay??).

there's a guy, Robert Aram, who has presented at solar conferences on soil conductivity and subslab insulation strategies. I'm going to try to chase him down and see if he has a gut sense of how he'd expect this to behave. (he'll be at the MREA Energy Fair this weekend, I hear)

so Mark - did you do any monitoring of soil temps to conclude there was no "heat bubble" or was that from just watching supply/return temps on the fluid going into the heat exchanger? and I'm guessing you weren't injecting the heat under a structure, or were you?

back to the drilling. what you did, Mark, sounds real close to what I am imagining. I was going to drill a hole in the slab (once I find an IR camera to help pinpoint tube locations). to get through my sand lift I was going to oversize and case the hole with PVC (a technique I've used before using a shop vac wand to suck out sand ahead of the PVC, drive PVC a little further, suck, drive, suck, etc). then I was thinking of either power drilling or using a hand auger to bore a slightly oversized hole the rest of the way. I was not thinking to go as deep as you did - maybe 5' overall - which would be 1' of sand and 4' of clay. what did you use for "grout"? - I was thinking about just a clay slurry, but would be better to have something that's not going to dry/shrink and pull away from the HX tube.

onward!

groundsource heat-dump solar trickle-charger?!?

@ June 6, 2011 5:03 PM in groundsource heat-dump solar trickle-charger?!?

Aloha!

have had a rather extended absence from this site but thinking about this question reminds me what a great bunch of minds & opinions are to be found here ...

OK here's the deal: my home, built in 1985-6. frost-protected floating-slab-on-grade 2 story. 24'x28' radiant slab on first floor (not too common back in 85!). polybutylene tubing (no PEX then) about a third of the way up in the slab. heat from freestanding wood-stove and slab. 9000 DD climate (N WI).

I'll spare the details of decision making but here's the slab insulation plan: 1' sand lift under slab above insulation/water barrier. 4" of foam around edge of slab and sand lift, 4' skirt of 2" foam outward to protect from frost heave, and underslab (undersand, actually) foam 5' in from perimeter (3" at outside edge tapering to 1" near center). this leaves a 14'x18' area in the center of the first floor where there is sand under the slab but no insulation. soil is heavy clay and, in retrospect, my sense is that this insulation strategy was not the best design choice, the ground-coupling would probably keep my house from freezing for a good long time even if unheated, but in normal conditions it makes for a real big heat suck, especially as I get the slab going again each fall.

til recently, slab was heated with wood boiler and off-peak electric. now the wood boiler is out (rusted out perhaps due to lack of O2 barrier in polybutylene??) and I have a new somewhat oversized solar DHW system (96 sf flat panels for a household of 1) in addition to the off-peak electric.

the solar system was intentionally oversized with the idea of trying to put some of the excess summer production into "preheating" the sand/ground under the slab. Bob Ramlow (and others) advocate high-mass solar charged systems which use an approach like this and take advantage of some of our late-summer abundant energy to get a running start into the heating season. the rub with my setup is I have no tubing down in the sand bed - its all up in the slab - and my guess is that I'd be doing a lot more overheating of my living space than heating of that big lump of cool clay under the house. I've thought about putting insulated carpet down on the center part of the house in the summer to resist overheating but that seems a bit clunky and still a challenge to get heat into clay rather than the house.

my latest Goldbergesque idea is the one I'm looking for feedback on. I'm imagining a few tube-in-tube "heat exchanger wands" stuck down through the slab, through the sand & into the clay (an interesting installation challenge, but doable, I think). I have a nice roughly 4'x6' hidden area under my stairs at the center of the house that could serve as the project area. I'm imagining ¾" copper tubes, capped on the bottom, maybe 4' (or more?) long, each with a internal ½" copper feed extending almost to the bottom (this concept inspired by the "butler solar wand" heat exchanger, the name of which I just now remembered.)

a small circ pump sends solar heat down to the bottom via the inner ½" pipe and on its way back up through the outer ¾" pipe would give up heat to the clay. over the course of the summer I am thinking a heat bubble will slowly expand out through the clay and result in a significant reduction of my slab-heating load, especially earlier in the season.

I invite comment on this idea. I'm not laboring under the delusion that this is going to "heat my house" as I'm sure most of the heat will end up flowing away from the house never to be felt again by me. but I am thinking that it could really cut into the annual fall & winter heat suck down into the 45°F clay abyss and thus be a worthwhile use of my extra summer solar BTUs.

whaddya think?

Roy

thanks, Tim

@ August 18, 2010 8:19 PM in BASIC CONDENSING THEORY ?

appreciate your time laying this out so succinctly!

I gained a better sense of the role that microprocessor controlled combustion nuances play in this technology.

left with the impression that modulation per-se doesn't necessarily increase efficiency (other than perhaps by reducing short-cycling), but that the subtle control of the modulation can add to efficiency by optimizing the whole combustion scene.

yeah

@ August 18, 2010 7:25 PM in BASIC CONDENSING THEORY ?

considering that one of the main selling points for the technology is the added efficiency through condensation, its really nice to get a sense of how/where that comes into play.

I'd like to see 2 graphs - one showing efficiency as a function of return temp and one showing return temp as a function of outdoor temp (for a "typcial" ODR curve)

as long as everyone's here

@ August 18, 2010 7:21 PM in BASIC CONDENSING THEORY ?

Tim - you said: "At 50% (roughly 20° to 30°F outdoor temp) of heating load same temps efficiency goes to 94% due to modulation and some condensing."

are you saying that part of the efficiency gain is due to modulation alone?

if so, how does that work?

OK, I'm getting it

@ August 18, 2010 7:12 PM in BASIC CONDENSING THEORY ?

the "partial load in %" axis is not load as a % of boiler capacity, but load as a % of design load. and then the supply/return temp lines are labeled for temps at 100% of design load and reflect increasing amounts of ODR as you move to the left.

that makes much more sense.

thanks ...

nice to see that concept in a graphical/visual mode ...

chris or tim or ?

@ August 18, 2010 6:18 PM in BASIC CONDENSING THEORY ?

can someone help me understand why, according to the chart for the Vitodens 200, the efficiency of the combustion process looks to more affected by the size of the load than by the return water temp.

one axis of their graph is labelled "partial load in %" which I would take to mean the actual load vs boiler capacity. if that's right, it looks like efficiency is much more enhanced by the boiler modulating down than by the return water temp dropping.

got a feeling I'm misreading this ...

dang

@ August 18, 2010 6:09 PM in A feel-good story

that may take the edge of my serious dislike of the yankees.

for a little while.

I can see each side of this

@ August 17, 2010 10:42 PM in Sustainability versus Eco-Bling

some eco/green stuff seems much more superficial than meaningful and that is both sad & frustrating

... and we're still in some of the early stages of the needed transformations, dealing with not-mature concepts & manifestations of "what's needed"

I live in an area that's hung a fair bit of identity on the "sustainability" concept, particularly using "The Natural Step" perspective, which came originally from Sweden. Karl-Henrik Robert, the Swedish doctor who is considered the founder of the Natural Step idea, came and spoke here once and the one thing from his talk that really stuck with me was his response to a question from the audience about compact fluorescent lights - asking are they a good or bad thing given the mercury they contain.

he said in his opinion its not a useful distinction to focus on whether they are good (saving energy) or bad (containing mercury). they are a step along the way from how things have been to how things will be. the more useful question is "do they move us in the direction we want to go, or are they a step backwards?"

which is to say not to hold things up to a standard of perfection - "is this the last word in what we need?" - and then find them lacking because they don't meet that high standard. but to appreciate that its all a process and each step along the way is not the completion of the process, but is a positive thing if it furthers the progression towards the ultimate goal.

so, by this criteria, the CFLs are good cuz they help with energy consumption, and are also imperfect with their mercury content, and leave room for further improvements.

for me, the biggest help from taking in this observation was to ease up on the judgments when I can see the imperfections in stuff, whether its eco-bling or whatever. hopefully it helps us along in the right direction. if not, then lets do it differently so it does help us along.

onward ...

a couple questions

@ August 15, 2010 11:44 AM in condensate dilemma

Mark -

I understand why neutralize if discharging into CI or on concrete or via acid-intolerant pump... but if into PVC drain where it will get diluted with other waste-water ... I'm not so sure why neutralizing is needed & most important.

why do you recommend a regular submersible rather than a condensate pump? is it the greater pump flow rate? the larger size that could avoid short-cycling from drainback from the discharge line when the pump shuts off?

outa the box

@ August 15, 2010 12:08 AM in condensate dilemma

with that approach! which I appreciate.

the rub there is that there's tubing in the slab, so I'd have to be pretty certain I wasn't going to hit it if drilling through the slab ...

probably a sand lift under the slab that could handle some condensate ... but clay below that, which would be quite slow to absorb anything.

might give that some thought though ... and then try to figure out how to be sure to not hit tubes ...

condensate dilemma

@ August 14, 2010 10:13 PM in condensate dilemma

helped a pal out by completing the install of a Quietside condensing water heater. he had hung it on the wall and I did the rest. its in a slab-on- grade duplex in a little utility closet that is between the two garages (heated) and the door opens to the outside.

one of my last things was to hook up the condensate line and look around for a floor drain. turned out there was none in the utility closet. each garage has a floor drain in the center but he told me they are just plumbed to daylight out 20' in the back yard. I'd be afraid that the constant trickle in our harsh northern WI winter would slowly fill the drain line with ice til it plugged. not to mention that the acidity would not be good for the lawn around the discharge point.

he's willing to discharge through the outside wall but again I'm dubious about freezing up, plus there's a 3' wide concrete apron that has to be crossed to reach dirt (I understand the condensate, unless neutralized, is pretty tough on concrete).

I'm wondering about a bucket of limestone chips for condensate neutralizing, then a condensate pump so that the fluid doesn't just trickle out but discharges a bunch at a time.

anyone recommend a model that comes with good safety switches so that if the discharge line gets blocked (by freezing or otherwise), it will shut things off.

or some other approach???

low temp radiators

@ August 2, 2010 9:35 PM in Solar Powered / Assisted Hot Water Radiators?

hr - can you give us any more details on the low-temp radiators that you mention. low-temp delivery is good for solar, good for condensing boilers.

I'm intrigued to find out what the strategy is on these to be more effective at low-temp than "regular" panel radiators.

myson gives these correction factors for figuring output from their panels for different air-water temp differentials:

output correction factor / delivery water temp less air temp
0.605 / 72˚F
0.700 / 81˚F
0.798 / 90˚F
0.898 / 99˚F
1.000 / 108˚F
1.104 / 117˚F
1.211 / 126˚F

flat plate drainback awning

@ May 27, 2010 4:30 PM in Solar Awning

(with PV on a tracker in background, facing west for afternoon sun)

awning mounts let you get an optimal slope in a way that usually looks pretty good. here too, like the evac tubes above, they can offer a secondary benefit as a window or door awning.