reset curves linear, radiator output nonlinear?

R. Kalia

I am confused about something related to outdoor reset. The reset curves I have seen are straight lines, going from 70 @70 to 180 @design temp (or something like that). But radiators and baseboard don't work linearly; the output at 125F (say) is not half of the output at 180F, even though 180-70=110 and 125-70=55. It is much lower than half at 125F.

So how does a linear reset curve work? Better than with a fixed 180 temperature but not very well? One must set a steeper curve than needed in winter, in order to handle spring and fall, and continue to use the thermostat to control temperature?

What is a "characterized heating curve"? How do you characterize the properties of the radiation in a given house, which may have a combination of types? What systems let you design a nonlinear curve? Munchkin? Ultra? Tekmars?

Mike T., Swampeast MO

Curves

By the math definition a straight line is still a classified as a "curve" but a curved line is not linear.

Lines have slopes.

What [seems] to happen when it comes to heating is that you get LOTS of "straight lines" at different slopes, BUT you can't always relate these lines directly to one another.

Heat loss calculations plot as a perfectly straight line with loss increasing by the same amount for each degree of temperature difference between inside and outside temps.

A simple mechanical reset does the same thing. It increases supply temperature by a fixed multiple for each degree of change in outside temperature.

Sounds great so far even if we do know that heat loss calculations are only an approximation and that sun, wind, rain, etc. will prevent the "real world" heat loss from being such a nice perfect line...

-------------------------------------------

Unfortunately our heat emission devices don't seem to work this way...

Fin baseboard emits about 3.86 btu/hr for degree of temp difference between supply and air when the average supply is 140° and about 4.96 btu/hr for degree of temp difference when supply is 190° average.

You can still plot baseboard output as a nice straight line, but it's not the same line as the "ideal" heat loss.

This is where "characterized heating curve" or similar comes into play. If you are stuck with plain mechanical equipment you essentially have to set a heat "line" higher than necessary towards the bottom to account for the lower output for degree of temperature difference. Electronic controls however can put these two straight lines together into an approximate curve that really does curve.

When it comes to standing iron radiators the "standard" published output tables only seem to be accurate at higher temperatures--say around 180°. If you follow them to low temperatures--say 90°--output goes to zero--ask anyone with a gravity conversion system with TRVs in an insulated home and you will find that this is IMPOSSIBLE!

----------------------------------------------------

Large, flat, very low temperature panels like floors are generally assumed to give off about 2.5 btu/hr for each degree of temperature difference within their normal operating range.

R. Kalia

thanks, but...

Thanks for the detialed explanation! But my question is, since radiators are nonlinear, why are reset curves usually linear, and which boilers or reset controller manufacturers have ways to set up nonlinear reset curves. The ideal would be constant circulation in all weather, but this can't possibly happen with a straight-line reset curve.

Mike T., Swampeast MO

We think along the exact same lines!

I know that some? most? of the Tekmar controllers do have non-linear curves and you "tell" them what type of output device is being used. Not sure about other controllers or boilers.

As to why reset "curves" are usually lines I can only guess that it's because they're easier to make, less expensive and that such is often good enough.

Don't forget that heat loss is only going to be linear in the laboratory and is influenced by many more things than temperature--yet temperature is usually the only control variable.

Constant circulation seems to come in a number of varieties.

If your system is of high volume and/or mass, you can use this volume/mass as a "flywheel" by circulating the water constantly and using a thermostat to control the firing of the boiler. You don't even need any reset control as the supply temperature will automatically vary with changing conditions. If your system has extreme mass (like most radiant panels) this can be a problem with rapidly changing outdoor conditions. If the system is still massive (but not so much as a radiant panel) you also have to balance short-cycling with space temperature fluctuation. To keep burn times reasonably long you often have to accept larger temperature swings. Oversized boilers will aggravate the short cycling condition.

I suppose you could do this with low mass devices like fin b/b, but they're going to give off all of the available heat very rapidly after firing stops and supply temp will also rise rapidly when firing begins. You don't get much of that "automatic" reset, so you're better off using reset controls to keep the supply temp down during moderate weather. Those controllers with true curves would seem to have a good advantage in this case.

Another strategy is injection mixing. You can add (inject) heat (via a circulator) to the system. Numerous ways to control this but the most straight-forward would likely be fixed injection where the injection circulator adds a fixed amount of water as dictated by the thermostat and the reset control; e.g. you keep injecting until you either hit your reset temp or the t-stat is satisfied. Variable speed injection will add a variable amount of water depending on the available temp at the boiler and the desired temp of the reset control--as long as there is a digital thermostat, it will have the ultimate control.

Yet another method of constant circulation will always be heating the system to the temp called for by the reset control. To prevent overheating proportional flow devices (like TRVs) are used at each output device. With a decent reset curve (even a straight line), the total flow through the system will be quite consistent regardless of indoor/outdoor conditions.

All of these methods will find constant circulation through the system whenever heat is required by the structure--sometimes even without a reset control. What none of them do however is provide a constant, perfectly suited level of heat in the supply.

If you're adjusting space temperature with digital thermostat(s), an electronic, non-linear reset control will serve to keep the space temperature swings as long in time and short in magnitude as possible. Some even have a "boost" feature that allows the supply temp to rise above the "normal" curve--useful when recovering from setback.

If you're using TRVs or similar, electronic non-linear reset is almost overkill as the valves will compensate for any supply temp overshoot automatically.

---------------------------------------------

Output devices tend to be tested in highly controlled and generally static laboratory conditions. All output tables I can find show an increasing output per degree of temperature difference as difference between the air temp and device temp increases. In general, it seems that the more convective the device, the greater this effect and the more radiative the device, the less this effect.

The exception to this seems to be large radiant panels which from sources I find at least are assumed to have a flat output of 2.5° per degree of temperature difference. Perhaps this is because the temperature of the panel is typically in a VERY tight range--perhaps it is because testing of such is extremely difficult.

Just how well output curves jive with real-world conditions seems unknown as the systems become too complex to model.

One thing that can be demonstrated mathematically is that the radiative output of a device does not stay the same--even at the same temperature of that device. The more closely the output of the device matches the actual heat loss, the higher the amount of radiation. What I do not know however, is if there is a perfectly corresponding drop in convective.

Electronic reset controls are essentially an attempt to make a digital thermostat behave more like a proportional thermostat.

Back to a statement of yours, "...ideal would be constant circulation in all weather, but this can't possibly happen with a straight-line reset curve."

Again, you can have constant circulation with a straight-line curve. If your system is digitally controlled, you still have thermostat(s) to prevent excessive overheating; if proportionally controlled, the reset becomes mostly a way to keep boiler jacket and/or transmission losses to a minimum.

Sorry for the extremely long-winded response--there just doesn't seem to be a simple answer.

Mark Avron

reset curves

A "fixed" linear heating curve has to be set high enough to satisfy your worst case senerio (i.e. baseboard, hydro-air, under-ratiated zone, whatever the case may be.) This type of conrolling can be used with traditional on-off thermostats and does create a more comfortable system than simple high-limit (180) boiler control. Running lower water temperatures will give longer on time of your zones and create less temperature swing. As far charatorizing a curve to a specific system, manufacturers give you guidelines but every application is different. Idealy you you'd start your curve low and adjust up from there. However this can be impractical (unless this is your house) so in most heating curves get set higher than needed. Mrs. Homeowner never calls when she's warm and toasty.

Having a "fixed non-linear heating curve" wouldn't do you much good either because heat-loss is dynamic. A 30 degree day does not always require the same water temperature. What you need is a dynamic heating curve. This is accomplished by using indoor temperature feed-back(room sensor) to compensate for internal and external gaines and losses (i.e. sun, wind, people, appliances, cooking, computers, lights, open doors etc.). The outdoor sensor gets you in the ballpark and the indoor sensor fine tunes things. Combine this control method with radiators that use TRV's and you have about as comfortable a system as it gets. TRVs are not just high-limit controls they also adjust the flow rate through the radiator. So now you get a combination of modulated water temperature and modulated flow. Keep in mind that outdoor temperature is used by reset controls as a reference point but ultimately our concern is accurate and consisant indoor temperature control.

Mark Avron
Buderus Hydronic Systems

S Ebels

Nice!

Couldn't have said that better myself. The heart of the issue is INDOOR temp control and how to make it happen as economically as possible. Nice explanation on the relationship and the neccessity of both outdoor reset and indoor feedback.

leo g_13

Mark

do not the TRV's act as indoor sensors for each emitter? and if so, why then add an electronic indoor sensor that may be only "centerally" located?

Leo G

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hydronicsmike

Great Question

You know, I was wondering myself why over all these years a "Reset Curve" was called a Curve, since it always was a straight line. When I moved here from Germany and learned the English language (well, as good as I could...), I simply figured it would be another one of those things, kind of like "football". Here we have a sport that is deemed to be "football", but if you actually follow the game, you note that the only time the foot is actually getting close to the ball (not a ball either) is when they punt it. When I follow the game, I find that throughout the majority of the game the ball is either thrown or carried across the field. But then, "Carry the ball" must have been taken already.

Anyhow, when it comes to Reset Curves, I always figured it was just another one of those things...

"Characterized Heating Curves" are not just there to actually make or create a Curve to do the name justice. Those are engineered values that allow us to match the heat output characteristics of each Individual Heat Emitter to the actual Heatload requirement of a building or space.

As mentioned in one of the posts above, a 'straight' Reset Curve does not always provide the right amount of heat, simply because of the different heat emitters don't all have a straight water temperature - heat output relationship. Fin Tube Convectors (most commonly referred to as Baseboard), for example, will have a significant amount of Heat Output loss at lower supply water temperatures. In order to eliminate the drop off in Output, we would need to raise the water temperature slightly under small load conditions, in order to get the output we need. A Fin Tube Convector needs a certain water temperature in order to keep the convection process going. A 'straight' reset curve would simply lower the water temperature to the Heat Emitter linearly based on outdoor temperature, but this could cause underheating in the spring and fall months, where we would be fine during colder days.

I hope this all makes sense. I know that I am not always the best trying to explain something in writing, using my geringlish (German and English combined:) ) So for your convenience I have attached an Essay on Characterized Heating Curves, that may explain those a little better than I could.

All tekmar Controls (since '99) come standard equipped with a Characterized Heating Curve that can be selected based on the heat emitter used in your Application.

Regards,

Mike

hydronicsmike

Great Info from Mark...

...The location of the Indoor Sensor is critical. If you only have a single one, you have to know the right place for it to be. Because anything that this Sensor reads would affect your entire system, as the Control is controlling and changing the water temperature based on its feedback.

Indoor Temperature Feedback is the secret to any comfortable and Energy Efficient Hydronic Heating System. There simply isn't anything better than combining Outdoor Reset with Indoor Feedback.

Personally, I like to promote Zone Controls that can have multiple Indoor Sensors for multiple Zones. I find that not always would the Indoor Sensor be at the right location. As mentioned before in another post, The Heat Load is always changing based on whats going on outdoors. For example, some parts of a building may get exposure to sun in the morning, where others do in the afternoon or evening. Some areas may be affected by external (solar) heat gain, where others aren't. When you can use multiple Indoor Sensors, one for each zone, a smart Zone Control can always chose which one of the Sensors installed requires the most heat and the Control would deliver the right water temperature to satisfy the zone that has the highest heat requirement at this time. Since Sensors are used to measure the Space Temperature, a smart Zone Controller with this type of feedback would be able to cycle the other zones for their requirement and the water temperature that is used.

I have attached another Essay that could clarify some of those things.

Again, I am hoping this makes sense.

Regards,

Mike

S Ebels

Yes but...........

The TRV's act only as a high limit by restricting flow. What Mark was talking about is the fact that an indoor feedback control will actually change the water temp of the system. It will "over-ride" and adjust to a certain extent the existing reset curve which is programmed into the boiler control. This will give near perfect water temp provided the indoor sensor has been placed properly. It basically does what the original post was asking,which is, provide an actual curve or multiple curves based on what is actually going on inside.

Mike T., Swampeast MO

Fully TRVd systems do provide feedback in the form of delta-t and delta-p.

Using this feedback to adjust the supply temperature can be EXTREMELY complicated as there is no way to communicate the desired temperature setting back to the equipment. It becomes VERY easy for programming logic to fail in this situation--the usual result is runaway supply temp up to high limit.

Fully TRVd systems don't really seem to "fit" into any of the categories of reset/feedback in the essay posted in this thread. (VERY good essay by the way.) This doesn't mean that indoor feedback manipulation of the reset curve can't be useful--it just means that you have to be VERY careful when using it...

The space that is naturally the coolest (least proportion of output to loss--hope that makes sense) would seem to be the best location for a single indoor sensor. An interior hall without a heating device [might] be good as well--I'm not sure. However, if your reset curve with indoor feedback gets extremely close to "pefect" you might loose the ability to keep other spaces significantly warmer--the better balanced the system the more this is likely. Setback could also be a problem--unless you've set back the space with the feedback sensor, recovery is going to be extremely sluggish.

While some reset controls might be able the deal with a feedback device installed in every TRVd space, I would imagine that the law of diminishing returns would take over and that the system would become highly complicated and extremely expensive with little improvement in either comfort or economy. The main advantage [again in a fully TRVd system] would seem to be to allow the system to establish its own ideal curve with very little human intervention beyond initial "good guess" settings.

Mike T., Swampeast MO

Your GerEnglish is certainly MUCH better than my EnGerIsh!!!

I wish that the typical Chinese/Japanese writers of English instruction manuals were half as good!!!!

R. Kalia

Thanks for all the very knowledgeable comments, folks!

(a) We do have a converted gravity system, but can't use "indoor reset" (using thermostat to let water reach ideal temperature) because there are two zones. I am also not sure whether in our system we'll get wild temperature swings or a too-sluggish response, and I don't want to do an expensive experiment to find out.

(b) TRVs would be nice, but at ~$200/TRV installed, for us they add up to a lot of money.

(c) A separate Tekmar appears to be the way to go, which eliminates Munchkin, Ultra and other systems that are packaged with reset. Tekmar also makes units with an indoor (in addition to an outdoor) sensor; very little information on their web page about how they work, but presumably they boost the water temperature based on the indoor reading, somewhat like "indoor reset" with a thermostat might do.

Mike T., Swampeast MO

Mfgrs. of modulating boilers (Munchkin, Ultra, Vitodens, etc.) seem a bit tight-lipped about how their control programs work. It does however seem that their method of reset is anything but simple...

Last fall a heating guy wrote about a gravity conversion system in a home under full renovation. A modulating Munchkin was recently installed. It was getting cold, the workers wanted heat but there was no thermostat around so he just jumped the thermostat connections and let the unit run off of his "best guess" reset curve.

Next day it was a bit warm and he adjusted the curve down a bit. After that he said that the temperature was even and consistent throughout the house despite workmen coming and going and other rather unusual circumstance. He observed the burner and found that it will operating in an inverse of the solar cycle--by itself and without a thermostat.

My own system is a gravity conversion with mechanical reset and TRVs on all the rads. Baths however have floor heat and are literally just tapped into the constantly circulating mains. No thermostat or variable flow control whatsoever in the spaces yet they stay perfectly comfortable and amazingly consistent in temperature--even moreso than the TRVd spaces! My reset "curve" (a straight line of course) is based on the assumption that the output per degree of temperature difference on my iron radiators stays perfectly consistent within their normal operating range.

In neither case do I believe that a truly "perfect" reset curve has been set. The Munchkin may or may not be "tweaking" this curve via its programming--I'm not sure.

I most sincerely believe that in both cases the mean radiant temperature of the space (as influenced by the sun, wind, rain AND occupancy loads) is taking some form of control of the output of the system--automatically and without intervention--and (it seems) nearly perfectly...

R. Kalia

football

> When I moved

> here from Germany and learned the English

> language (well, as good as I could...), I simply

> figured it would be another one of those things,

> kind of like "football". Here we have a sport

> that is deemed to be "football", but if you

> actually follow the game, you note that the only

> time the foot is actually getting close to the

> ball (not a ball either) is when they punt it.


Well, I had the opposite problem. I could not understand why, when the rest of the world plays football, the ball is round instead of being shaped like a foot the way a football should be. Fortunately, you have now explained it to me: kicking the ball with your foot = football, what a concept!

ScottMP

Great Job Mark

Nice to see your name here "old boy ".

Scott

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hydronicsmike

RPG

Indoor Feedback is described in the E004 Essay that I attached to one of my posts above. Please read through that and let me know if I can help you in any way.

Regards,

Mike

hydronicsmike

Thanks Mike...

...for your comment.

R. Kalia

Acrobat says "File is damaged and cannot be repaired". I was able to read the other file (the one from Tekmar about their characterized heating curves) without a problem.

hydronicsmike

I don't know why it doesn't work for you...

....I tried and could open the same file on my PC. Maybe try getting it directly from the web site at www.tekmarcontrols.com.

Once there, click on the "Downloadable Literature" Link -> "E Brochures" -> select "E004 - Control Strategies for Building Space Heating" in the drop-down menu.

I could get it to work both times. You may have to upgrade your Adobe Acrobat Reader. The latest, free version, can be downloaded directly off their web site at www.adobe.com. The latest version I know of is 6.0.

Please let me know if you have more troubles.

Regards,

Mike

Robert O'Connor_3

Try This

RPG,

Try this: http://www.tekmarcontrols.com/

Jed

R. Kalia

That worked, thanks!

hydronicsmike

Perfect!!

You're most welcome!! Have a great evening.

Boilerpro_3

One thing being forgetton here, IMHO

Is that even if there are no variations in solar gain, wind speed etc. heat loss is not linear with the change in temp. due to the fact that the chimney effect through the structure, which causes most infiltration, ACCELERATES AS IT GETS COLDER. Heat loss due to infiltration is nonlinear.
I find it sort of funny that the highest tech controls now use heating curves adjusted for the output of the heating units. For nearly all (if not all) of the types of heating unit, the output accellerates nonlinearly with higher water temps.
With the heating units doing this and the accellarated heat loss due to stack effect, the old, simple linear curves probably better match the heat output of the system to the load, than the more sophisticated nonlinear curves.

Sorry Mike,

Boilerpro

hydronicsmike

I don't know how you figure that, Dave...

...but I am also not prepared to argue with you over this.

I am just basing my statements on facts that some very smart Engineers have come up with years ago. Having used those new 'sophisticated' "Characterized Heating Curves" in the last 5 years successfully, proves to me that the work the Engineers did paid off.

No matter what, and you'll have to give me more than the note you wrote, to convince me that the Heat Output of a Heat Emitter is linear to change in Water Temperature based on Outdoor Change. A Heat Emitter does NOT change its Output linearly. Hence the reason why some of those Heat Emitters (now, we learned) actually need a slightly higher Water Temperature than straight linear Reset would give you when a small output is required. Before, when the water temperature was reduced linearly to outdoor change, the heat output would just fall of more than desired. Think about it and try it out yourself...If you never had the problem with slight underheating (with straight reset curve / ratio)in the spring or the fall, your heating curve is set to high to begin with. One way to prove that, is to check the system on the Outdoor Design Day. If you walk into this building and all your thermostats are shut off at any given time, the Water Temperature is too high.

I am also not ignoring the fact that this would be an 'ideal' case that works on paper and may not work in the field, but you could and should be close to that.

Thats just my honest opinion as well and has nothing to do with any type of Controls out there. Some Controls just address the issue. Why else would a Characterized Heating Curve exist today? Because we needed something 'new'? Nope, because we steadily want to improve Energy Savings while still maintaining the highest comfort level possible by eliminating temperature swings and expansion noises.

Sorry Dave.

Mike

R. Kalia

but the Tekmar 370 is incredibly expensive

The basic message of the tekmar handouts is, their products are the best. This is may be true. But handling a multizone hydronic system with indoor feedback seems to require a Tekmar 370 and several indoor sensors. Cost maybe $700-800 just for the hardware.

For a single zone, "indoor reset", as described by Mike T above, seems like an elegant and cheap idea. You don't have any controller other than the home thermostat. The circulator is wired to run all the time; the thermostat turns the boiler on and off. The result is that the water reaches and holds the perfect temperature needed to heat the house (it never reaches the fixed aquastat setting, which can be left at 180). Unfortunately it doesn't work for multizone systems.

hydronicsmike

It is expensive, no doubt...

Indoor Temperature Feedback for multiple zones has it's price. But it's overall Efficiency and Comfort level are hard to beat, if at all.

In your case, however, I believe you were talking about using those Fin Tube Covectors (Baseboard) or Radiators with Thermostatically Controlled Radiator Valves (TRVs), right? If thats the case, you could install a Radiator or Baseboard without a TRV in the space that you deem to be the most appropriate and hardest to heat place in the building. Then install a single Indoor Sensor to a Mixing Control, like the 360, 361 or 362 maybe (depending on Mixing Method preferred), that will give you Mixing and Constant Circulation with Full Outdoor Reset and Boiler Protection, if required. The Zone without the TRV will get the constant circulation and Indoor Feedback from the Sensor, where all other Radiators or Baseboards will have their TRV for independent Room Temperature Control. The TRV would basically throttle the amount of flow through each Radiator or Baseboard based on Air Temperature.

I hope this makes sense. If not, please let me know. I'd be glad to help, if I can.

Regards,

Mike

Mike T., Swampeast MO

That "elegant and cheap" indoor reset via wall thermostat has some severe limitations--particularly when it comes to efficiency.

It offers zero protection from low return temperatures. If you have an older cast iron boiler that is typically oversized this [usually] isn't a problem, but it brings up all kinds of poor efficiency issues. Since it's oversized you either have to accept larger than normal temperature swings or shorter than normal burn times at the boiler. Both take their toll on efficiency. With the rapid burn cycles and lower than normal temperatures the boiler is probably working will below its rated efficiency as well.

This won't work with really old, high volume boilers that have to be kept at at a certain temperature lest there be a huge time lag between fire and delivery of heat.

With most modern cast iron boilers (particularly if properly sized to the house) you really have to start worrying about low return temperature, so it won't work with those either.

If your current boiler fits into the "older, oversized, cast iron" category, and you want reset with your two-zone system, a mechanical model should be all you need. Those that offer adjustment for both slope and base are best. Not expensive and very long-lived. Should be a variety of manufacturers--around here I find White-Rodgers. This should give you a noticeable reduction in fuel use.

If you're planning on replacing your boiler soon, I'd give utmost consideration to the finest condensing (or condensing/modulating) boiler that you can possibly afford. Protection from low return temperatures becomes a non-issue as does the reset "thing" with the modulating varieties--such will already be built-in.

Boilerpro_3

Oh I agree with you Mike

Heat output of a heat emitter is non-linear, it accelearates as the temp in the emitters rises( I suspect mainly due to increased convection currents), making the curve slope upward. However, what I was trying to point out is that heat loss is also nonlinear with the change in temp, due to the accelerated heat loss at lower outdoor temps. A house is just another heat emitter on a cold day and it responds nonlinearly just like the heat emitters in the house. The greater the temp difference between out and in, the stronger the convection current (Chimney effect) there is through the stucture. The number of ACH increases at cold temps which multiples the effect of the greater delta tee. At 40F, a typical medium tightmess structure will have .7 ACH infiltration, at 10F it has 1.0 ACH infiltration... this is right out of the ASHRAE design tables.

Example:

A structure with an interior volume of 10,000 cubic ft.

At 40F outdoor the heat loss due to infiltration would be:

10,000cu ft x .7 ACH x .018 x (70F- 40F)= 3780 btu/hr

AT 10Foutdoor ;

10,000 cu ft x 1.0 ACH x .018 x (70F -10F) = 10,800 btu/hr

A doubling of the Temp difference from 30 to 60 produces nearly a tripling of the heat loss.

So the old straight heating curves that allowed the natural increase in heat output to occurr at higher operating temps (when temps were lower outside) may better match the real world heat loss of structures.

Interesting, Eh.

Boilerpro

R. Kalia

Yes, of course, it doesn't work at all with cast-iron boilers. Which is what we have now, but we'll be replacing it. Probably with an MZ.

hydronicsmike

Dave...

...Sorry, I must have missed your point completely. I agree with you that the heatloss doesn't change linearly based on Outdoor change either.

Don't you just love it?? There is so much more to our bizz than pumping warm water through pipes.

Boilerpro_3

Ah...

Do you see how the old straight curves might actually work better....this is what I found so funny! A circa 1950 reset control may work better than the most sophisticated we have today!

Oh, well......


Boilerpro

hydronicsmike

Nope...

...that I didn't agree on. I agree that the heatloss of a building is not linear to outdoor change, but am sticking with the Characterized Heating Curve being a better match.

Boilerpro_3

Curious then,

> ...that I didn't agree on. I agree that the

> heatloss of a building is not linear to outdoor

> change, but am sticking with the Characterized

> Heating Curve being a better match.

Boilerpro_3

Curious then,

Are the curves designed to match an "average" increase in heatloss rate of a structure due to the acceleration of infiltration losses or are they designed to make the heating units respond linearly with outdoor temp?

Boilerpro

hydronicsmike

I would say...

...that with the Characterized Heating Curves, we will (more accurately) match the Heat Output Characteristics of a Heat Emitter to the Heatloss of a building at a given time.

There are a whole lot of variables to consider Dave, you know that...

Boilerpro_3

So it is a combination,

sort of figured (and expected)that, but you don't know till you ask.

Boilerpro

R. Kalia

question for hydronicsmike (or anyone else)

I have been studying the Tekmar documentation and it seems like the 370 is the one for me; it is very expensive but it'll let me avoid having about seven TRVs installed, so I'll come out even or ahead.

This is the 'integrated' box with zone control, plus outdoor reset plus multiple indoor temperature sensor inputs. It claims to determine the water temperature needed for the zone that needs the highest temperature (with continuous circulation in that zone), and turns the other zone circulators on and off. For our house this is just what is needed.

The documentation is minimal, however, and Tekmar won't take questions from end users. My question is, do these controllers have any reporting functions? None are documented. In other words, I would like to know what the current water temperature goal is, whether it has been boosted via the indoor sensor reading, which zone ran for how long, etc., etc. Given that there must be quite sophisticated electronics in it, this would seem to be an obvious capability.

Many thanks for any help!

hydronicsmike

Who says tekmar wouldn't answer questions to end users?

RPG, you are always most welcome to call tekmar if you have any questions. If you call between 7.30AM and 4.00PM PST at 250-545-7749, Ext. 214, I will take care of you. Just ask for Mike.

It seems the 370 could do, but no read out. There are different options that you have and I'll let YOU decide after we went over them.

Looking forward to talking to you.

Mike

R. Kalia

I was discouraged by the web page...

Oh, OK, these days I do everything by computer, and since Tekmar's web pages gave no e-mail address (and its web form is limited to literature requests) I figured the message was "we don't want to deal with questions".

I will call. Thanks!

S Ebels

RPG

I may have missed it somewhere up the line but, what boiler are you going to be installing the reset system on. Specifically, I'd like to know what type it is in order to determine what water temps you can run.

If you have a standard cast iron boiler you will have to purchase and install a motorized mixing valve in addition to the Tekmar. $,$$$.$$!!

You might want to consider some other options......