water flow rate modulation instead of outdoor reset?

R. Kalia

[My first plan did NOT make much sense, so I have deleted it. But please see my next attempt, below.]

hydronicsmike

My feedback would be that...

...it would work if you modulated the flow rate. If it wasn't for the operational losses that would still occur.

Lower temperatures, lower losses. It's the temperature difference between something (Pipes, Heat Emitters) and ambient. Most Boilers that I am familiar with are more efficient at lower temperatures. I can't really see the overall benefit of modulating the flow. Modulating the flow would be more like a thermostat that doesn't turn a device (Zone Valve, Zone Pump) on or off, but rather increases or decreases the flow rate. How would that take place? Probably with another Control. Replace one with another?

There may be applications for such a system you describe, but not your average Residence or Light Commercial Job, unless I am missing something substantial here. Our friends at Grundfos have the technology you're after in their hands, but ain't moving a whole lot of it as far as I know. Again, I may be wrong.

I've just always been a Reset Control guy and thats what I know and believe in. I would always want to conserve energy by allowing your equipment to run at the lowest possible temperature to increase its efficiency, but also to minimize operational and stand-by losses.

Mike T., Swampeast MO

Sort of, but some problems

"The point of outdoor reset is to control the amount of heat delivered, not by starting and stopping the flow of water, but instead by varying the water temperature at the boiler output."

That's more the effect than the point. To me, the point of reset is threefold:

1) To provide an anticipation of changing heat loss by monitoring outside temperature. The more massive the heat emission device(s) and the better insulated the structure, the more useful it becomes to take action before the insulation allows the loss to change greatly.

2) To introduce a dynamic (btus available) in the system that results in a fairly static condition (constant circulation).

3) To minimize ancillary heat losses from the boiler jacket, transmission piping and in the case of condensing boilers in particular the flue.

Ideally, when a system is designed the engineer computes the head loss (flow restriction) in the system and chooses a circulator that will deliver the required flow (velocity)at this level of restriction at or near the most efficient level provided by the circulator.

I don't claim to be an expert on the efficiency of circulators but I do know that some are designed to be more efficient when delivering high volume at low restriction while others are better at delivering low volume at high restriction. Start changing flow or restriction radically and you loose electrical efficiency and reduce service life.

If you keep constant circulation at a steady flow rate via reset you have the opportunity to make your circulator operate with very high electrical efficiency by sizing generously and keeping runs to a reasonable length. If you keep constant circulation by changing the speed of the circulator (to change velocity) you have also changed the flow restriction in the system. The circulator may or may not be operating at/near peak electrical efficiency--again I'm not certain how great the effect will be, but I'm quite certain that ½ speed = ½ velocity = ½ electric consumption is NOT true.

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"Even though the boiler output water is 180, the _average_ water temperature in the radiator will be the same as it would be with outdoor reset (since the same amount of heat must be emitted in both cases). The difference is that the return water gets colder as the flow rate decreases--which is a good thing if you have a condensing boiler. The return temperature will in fact be even colder than it would be with outdoor reset (where there would be a higher flow rate)."

Many boilers won't take too well to tinkering with the flow rate through them in this way. Copper tube boilers don't like it when flow is reduced and the brain of a modulating boiler that's looking at delta-t would very possibly have problems determining what is going on in the system--flame modulation may well become erratic or non-existant.

"No outdoor sensor or outdoor reset electronics is needed."

In many systems a simple, reliable and inexpensive mechanical reset (preferably dual-adjustable) is all that is required. Modulating boilers will already have reset ability built-in as an integral function of their operation and certainly won't take well to having this feature defeated.

"Unlike outdoor reset, changes in heat load (e.g.oven is turned on or the sun comes up) are handled nicely since the temperature sensing is done inside the house."

What if the temp sensor is in one space but the oven and/or sun in another?

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Just my thoughts on a VERY interesting topic.

R. Kalia

Plan B

I can't take credit for thinking of the following plan, but I'd like to bounce it off the experts here.

Instead of having the room thermostat relay controlling both the circulator and the boiler, it will control the boiler only. The circulator will be connected directly to power and runs 24/7. So now the boiler is cycled by the room thermostat and not the aquastat--set the aquastat to 180, but the water will never get that hot.

If that doesn't make sense, think about it: if 180 + constant circulation = too much heat for the house, then since we already have constant circulation, the room thermostat will turn the boiler off before the water gets to 180. What this means is that the water temp will balance out at exactly what is needed to hold the indoor temperature setpoint with constant circulation, no higher and no lower. But that's precisely what outdoor reset is supposed to do!

So we get the same result---water temperature as low as possible, and continuous circulation--as if we were using outdoor reset. We get this with no outdoor reset controller, and no setting or fine-tuning of reset curves.

In fact it is even better than outdoor reset, because the water temp is determined by the actual heat load, rather than outdoor temperature which is not always a perfect measure of actual heat load.

Will this work? It sounds too good to be true, and if it really worked, you guys would all be using it and Tekmar would go out of business. (Of course, it will only work with boilers that can take low water temps; and a modulating boiler is unnecesary----even if you have modulating burners they will always be on full fire.)

So what is wrong with this plan?

Mike T., Swampeast MO

Simple Constant Circulation WITHOUT Reset

Is what you've just described. Your mileage may vary...

Constant circulation is often regarded as a method that both increases comfort and decreases energy consumption. But how can that be when you increase electric use by running the circulator continuously?

It can only decrease energy consumption if it somehow decreases loss and/or consumption in other parts of the process.

Since the supply temperature is cooler you have reduced jacket losses, distribution losses and flue losses (condensing boiler at least). But that's just PART of the story.

If you manage to circulate just the number of BTUs being lost at any given moment in the structure your system is operating at absolutely peak efficiency.

But how can you determine just the number of BTUs being lost at any given moment? That's the $1,000,000 question but it WON'T be answered with a digital air-temp reading wall thermostat--ever.

Why? The molecules of air have LOTS of energy--unfortunately they have so much energy that they can't stand to be near one another at normal temperatures and there's just not much matter contained in air. Air becomes nearly transparent to heat in the form of radiation.

Why does radiation matter? Because radiation is the DRIVING FORCE OF HEAT LOSS IN A STRUCTURE. This is such a simple concept known for so long that we actually forget that it is happening. Why do you think that infiltration is the major "unknown" and the most difficult part of heat loss to contend with???

It's been said over and over, but our body IS a radiator. To be comfortable it must be radiating energy. Air temperature has less to do with human comfort than a wall thermostat leads us to believe.

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Let a digital wall thermostat control your simple constantly circulating system and the burner is now a slave to air temperature in the space. The air temperature will yo-yo at the degree of accuracy allowed by the t-stat. OK--sounds fine with an accurate t-stat. BIG PROBLEM THOUGH!

The air in a space is in constant physical motion. Unless your heat emission device is absolutely massive and extremely low in temperature it WILL encourage convection. Convection means motion that we can detect with our senses. While convection may be wonderful on a hot day when everything surrounding us is too hot, it's awful when everything surrrounding us is too cold!

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You have NOT increased space heating efficiency or comfort by combining a simple constantly circulating system with a digital wall thermostat. An extremely massive system doesn't really benefit by the continuous circulation in this instance as it is able to absorb the BTUs even if the circulation is irregular. Systems with extremely little mass don't benefit either as they liberate all of their heat very quickly.

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NOW give your system feedback based on the temperature OUTSIDE...

First, remember that insulation only SLOWS heat loss. I believe it very safe to say that insulation results in a time lag. With outdoor reset you are able to anticipate a changing demand from the outside BEFORE it appears in the air temperature inside.

To make constant circulation as efficient as possible remove ALL forms of digital control. TRVs and other proportional flow control devices when used on a constantly circulating, reset system are essentially COMFORT ONLY devices. A modulating burner is [IMO] the most efficient thing that can be added in terms of energy used to heat the structure.

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There must be damned good reason that every residential condensing/modulating appliance of which I am aware uses OUTDOOR reset as an INTEGRAL part of the modulation program. Some might offer indoor feedback in addition, but only to alter the OUTDOOR curve.

p.s. unedited rambling stream of consciousness

R. Kalia

but...

> Constant circulation is often regarded

> as a method that both increases comfort and

> decreases energy consumption. But how can that

> be when you increase electric use by running the

> circulator continuously?


Circulators don't take much power...about as much as a light bulb, around 100 watts. Continuous (or rather near-continuous) operation is an essential part of outdoor reset as well.

> But how can you

> determine just the number of BTUs being lost at

> any given moment? That's the $1,000,000 question

> but it WON'T be answered with a digital air-temp

> reading wall thermostat--ever.


Many residential hydronic systems are controlled by wall thermostats. The wall thermostat generally controls both the circulator and the boiler, whereas in the proposed system it would control only the boiler. But in both cases only temperature is being measured and used for control.

So I don't understand your objection to the proposed plan---any problems with a wall thermostat would be present in any hydronic system using such a thermostat, not just the proposed one.

Mike T., Swampeast MO

Not really an objection--just a belief that the outdoor temp is a better way to anticipate the BTU loss of the structure. That's essentially the way I control my house with the exception that the thermostat is outside.

Not only did that outdoor thermostat cost no more than a nice programmable indoor thermostat, but it provides a proportional control means instead of just "on-off". I suppose it would still work reasonably well if I controlled the boiler fire with an indoor thermostat, but it seems much easier to me to place an outdoor sensor to measure a truly representative temperature than an indoor.

Remember that a condensing, modulating boiler like the Munchkin is doing its best never to satisfy the thermostat and it requires a "guess" (the outdoor reset curve you have set) to do this.

In the proposal, the firing time of the burner will tend vary with the outdoor temperature--the warmer it gets outside, the shorter the burn time. If the proposal received temperature information from the outside however, the burn time would tend to remain constant with only the time between burns varying with temperature. Neither are an ideal situation but if you imagine the graphs of each I think you will see why modulation, outdoor reset and constant circulation are a wonderful match--a match made even better if your emission devices are proportionally controlled.

R. Kalia

If you think about the system I described, you will see that it achieves the same goal as an outdoor reset---continuous circulation using water that is as cool as possible. It uses "indoor reset"---it is NOT 'continuous circulation without reset'.

It is NOT true that with the method I described, the warmer it is outside the shorter the burn time. In this method the thermostat, not the aquastat, determines the cycle time. The thermostat cycle time depends on its dead zone. If the room is held at 70 +/- 1, then the burn time is determined by how long it takes to heat the water up enough to heat the house by 2 deg., which depends mostly on the heat capacity of the house and only very weakly on the outdoor temperature. The time between burner cycles does depend on the outdoor temperature, just as it does with outdoor reset.

It is true, it does not anticipate. But let's say there is a three-hour time lag due to insulation. The hydronic system does not take three hours to respond. So outdoor reset will warm/cool the water well before a change is needed, resulting in a too-warm/cool room. Indoor reset will change the water temperature only when it is needed.

And by the way, outdoor reset doesn't measure the radiative heat transfer in a house either. Nor does it measure temporary changes such as changes in the number of people in the house, door open, oven on, sun shining in, etc. It's a little like trying to measure how many people are in the house by counting the number of cars parked outside---not a bad way to estimate, but actually going inside the house and counting would be more accurate.

I realize that everyone 'knows' that measuring outdoor temperature to reset the water temperature is the way to go. But it may be merely dogma---conventional wisdom. The method I described has not received any airtime until now because you can't do it with cast iron boilers (water will be too cold), whereas outdoor reset is possible with CI if you set a lower limit or use mixing valves.

hydronicsmike

RPG

You are an interesting man. I see that you are thinking about this very hard and that you are trying to re-invent the wheel and/or to put heat-timer, tekmar and whoever else there may be out of business. Your thinking is not wrong when it comes to your proposed logic, but what about the following:

You say that all we need to do it use a condensing (low temperature) boiler and a single thermostat. Boilers Aquastat set to 180°F (?) and the thermostat cycling the Boiler on and off while the circulator is running continuously. This may work in a single zone application. So far, no problem, as long as the thermostat is set to 70°F that's what we'll maintain.

Now! What if anyone turns that thermostat up to 95°F, what will the temperature in the space be? I'd be darned if it wasn't 95°F. Isn't the purpose of Outdoor Reset to limit the amount of heat that is being put into a building? In other words, it should (technically) always maintain your indoor temperature at a normal comfort level of 70°F. The thermostat would (technically) only be a limitting device that is used to lower the temperature in the space below that. Wasn't this one of the reasons it became so popular in residences and commercial applications? In an Appartment building, for example, with Outdoor Reset we can make sure that you don't get a tennant setting the thermostat to 90°F and then open the windows to control the temperature in the space while you, the Appartment owner, are stuck with the heating bill.

If you want more points, let me know and I'll get you those too.

Again, it is an interesting idea and I don't neccessarily dislike it. But I just can't see it being practical. I bet you that if it was as simple as you describe, it would be done. Outdoor Reset takes care of everything, plus it eliminates the possibility of someone sticking you with an outrageous energy bill. Nevermind looking into multi-zone systems.

R. Kalia

good points!

Yes, multiple zones are indeed a problem.

As a homeowner with a single-zone house, I wasn't thinking of the issue of preventing renters or whoever from wasting energy. I was thinking only of my own case.

So both your objections are excellent ones for the relevant cases.

Thank you for the compliment, but the idea is not mine, it is being fed to me (so to speak) by someone who has been in this business a long time. I am posting it here because I don't have enough experience to catch hidden problems (like the ones you caught, but those are not a problem for me).

hydronicsmike

RPG

Again, I like what I read!! Good job educating yourself....and that for a homeowner who doesn't deal with this on a daily basis.

I do believe (and like to argue) that Outdoor Reset is a very good indicator of the heat load of a building as we know that the load of a building changes when the outdoor temperature changes. Its the temperature difference between indoor and outdoor temp that determines the load (plus insulation, windows etc.). You're right, it is a good guess but not dead on (neccessarily accurate).

Most Reset Controls that tekmar makes can have an Indoor Sensor hooked up to them to gain indoor temperature feedback for single zone systems like yours. A thermostat is nothing but an on/off switch. A regular Reset Control, if used with a thermostat, can only know that now we need heat (thermostat calls) or now we don't (thermostat stops calling). It never knows how much heat you really need. So all the Control can do, is give you a water temperature that is determined by Outdoor Reset. In most cases, this temperature wil be +/- 10°F within what you actually need.

Now, with an Indoor Sensor connected to a Reset Control for a single zone system, the Control now provides continuous circulation and is able to fine tune the water temperature not only based on Outdoor Reset, but also based on Indoor Temperature feedback. With a Sensor in the space, the Control always knows what the temperature is that you would like to maintain and the temperature it is currently. With this information, the Control can provide you with the exact water temperature required to give you continuous cuirculation and the lowest water temperature possible.

That all translates into providing maximum efficiency and lowest distribution losses and no temperature swings (and expansion noises, depending on what type of system you have).

There are Zone Controls available for Indoor Feedback for multiple zones. I've been in this business for a little while myself and find that most homeowners will not shy away from spending the extra money to get Indoor Feedback, if explained properly so they can understand what it actually does.

You're right, you can count the cars in front of the house to estimate how many poeple may be inside. But you never know for sure unless you go inside and count them. I like that example!!! -I hope some readers are will make use of this quote in the future. Where do you come up with this??

Unknown

like this?

http://www.exqheat.com/pages/707613/index.htm

R. Kalia

Hmm. A very strange web site. They are trying to do, in a complicated and time-delayed way, exactly what the plan I posted does simply, directly and without much lag.

Mike T., Swampeast MO

Always wonderful to question...

...I know I certainly do it, and I certainly don't claim to have all of the answers (not saying that you claim to). Guess I just enjoy the brain exercise.

The idea of "indoor" reset certainly isn't new. Until the 70s or so, most residential water boilers held LOTS of water and had a HUGE HX--so much that just the time required to heat HX would introduce an unacceptable lag in heat delivery. So, these boilers were always "on", keeping their contents heated to the setting of the aquastat and waiting for the thermostat to call and turn on the circulator. Even here there is a sort of "reset" as the average temperature of the radiators will rise as the temp falls outside.

I'm not sure when outdoor reset controls for residential boilers first appeared on the market, but I do know that even boilers of this type sometimes had them. More than anything, such served to reduce standby loss from the boiler itself because it wouldn't be constantly heating water to 180° or so when only 120° (or cooler) water was needed. Boilers like this last for decades--even with return temps so low as to make a modern heating engineer flail his arms shouting, "Danger. Danger. Danger".

After this cast iron boilers got significantly smaller--the HX was smaller and they held a lot less water. Since the HX could be heated quite rapidly, it no longer made sense to keep the boiler producing hot water continuously, so it became very common to have the t-stat control both the burner and circulator in unison. Again, you have "indoor" reset as the boiler will rarely if ever reach the aquastat setting--the aquastat becomes more of a "high limit safety" than anything. The supply temperature will vary just as you describe, gradually increasing as the outside temperature drops. This is completely independent of the operation of the circulator--it doesn't matter if it runs continuously or rarely, the supply temp will still vary with outdoor temp.

Again, outdoor reset was often incorporated into these boilers. If you adjusted the reset curve so that the boiler "hit it" and stopped firing during most typical calls for heat, you wound up with longer and longer periods of circulation which helped keep the temperature fluctuation in the space in longer and longers periods between "high" and "low".

Even before the ability to get "flame on demand" boilers had "reset". It was called YOU! While some of the really fancy models may have had automated mechanical controls to vary the draft inversely with indoor temperature, most relied on the operator to determine how big a fire to build and how much oxygen the fire was allowed to access. Rather interestingly, this was a proportional system with constant circulation and OUTDOOR reset! Why do I say "outdoor" reset? Because if it got really cold outside you built a bigger fire! Why did you build a bigger fire? Because you knew it would be needed in a little while. If you waited too long to increase the size of the fire (it got too cool inside), you essentially had to get a rip-roarer going, overheat the house and maybe even open the windows if you waited too long to drop the size of the fire as the space or the temp outside warmed. Again, this was done without concern for low return temps and such boilers last decades.

I know full well that outdoor reset doesn't measure the radiative transfer in a house--even the most accurately designed reset curves aren't going to be producing just the number of BTUs needed by the structure. However, there really does seem to be a strange relationship between heat removed from the system and heat available to be removed when your control is proportional, of reasonable mass and with a reasonable amount of radiative output. Some of the "unneeded" heat never makes its way out of the water into the space--how much makes it out? It depends on two things--the ability of your heating device to radiate and the mean radiant temperature of the space. Never forget that you, the oven, those light bulbs, etc. are just as important to mean radiant temperature (and exercise the same sort of control) as the walls, floors and ceiling...

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Again, remember that the early central hydronic heating systems generally had no thermostat. You had a handle connected to a chain connected to a draft damper. This was essentialy a "warmer-cooler" adjustment but you STILL had to be wary of what was going on outside lest you over or under-shoot the inside temp like mad. This WAS a proportional, modulating, outdoor reset system.

"Flame on demand" and digital wall thermostats changed all of this. Gone was the proportionality. Gone was the modulation. Gone was the outdoor reset.

Little by little, we've figured out how to bring these elements back into modern systems. TRVs (proportionality) has been around for decades--so has outdoor reset. The final element, flame modulation, was the most difficult however. Now we have it--as long as the technology proves to be long-lasting--it is wonderful. But guess what? Once we have returned to truly automatic proportional, modulating, outdoor reset systems, the need for that wall thermostat (not outdoor reset) seems to be the thing that is no longer needed. Again, all we need is a "warmer-cooler" adjustment--just like way back when. But now its BETTER. It's now so automated that temperature swings in the space are a direct reflection of the solar cycle as delayed by the insulation! As long as you don't have an extreme amount of excess solar energy entering or an extreme amount of heat added by occupancy, you'll rarely if ever experience a comfort problem because of air temperature or air movement. And you'll use less energy to be even more comfortable as well!


I love it when technology goes "full circle" like this!

R. Kalia

Yes, a reset controller with indoor sensor should work well. The thing about the idea I posted, though, is that it doesn't need any fancy electronics.

Unknown

You want simple?

I still say temperature reset is a better way to do it. If you are against controls, think about this method. Keep in mind, I'm being simple on purpose.

Pipe the boiler as a primary loop. Pipe the radiation as a separate constant circulation loop. Feed water to this loop with an injection pump and balance the injection return to the primary loop with a valve such that when the system is stone cold, the boiler is able to come up to temperature and not condense (if that's the type boiler you use).

Run the injection pump AND the boiler from the room thermostat. Run the loop constantly.

Indoor reset, no electronics, load feedback, boiler protection, cars in the parking lot.

Noel

Sorry, Mike. I still like your stuff. This is just conceptual.

Mike T., Swampeast MO

Noel

What are you apologizing for? I keep running off on this theoretical, proportional radiation tangent...

Your proposal is certainly workable even if you don't believe it ideal yourself.

hydronicsmike

Noel...

...no matter what, we will always love you too.
How's things?

I believe in doing it right. It's the Mickey Mouse people who have hurt this trade and it's proud craftsmen enough as is. But thats just my opinion.