Heat loss calc ?

Mike T., Swampeast MO

114 mbh Manual-J loss; 91 mbh INPUT from the 6-24 Vitodens and I'm 100% certain that it will MAINTAIN 70°F indoors with outdoors SUSTAINED at 5° below zero (13°F below design).

Could I raise indoor temp in those conditions. NO!

Want "insurance"? Just specify electric resistance heat in the A/C system(s). Little additional cost. Convenient, tolerably comfortable and quite efficient in shoulder seasons when all you really need to do is remove the morning chill from the AIR.

S Ebels

Heat loss calc overage?

I have been using HVAC calc for all my heat loss calculations for the past 4-5 years and have repeatedly found that the hydronically heated homes we do are over radiated. The forced air systems we put in seem to operate as one would expect when properly sized.

Here's a couple of examples of what I'm refering to in the hydronic houses. House 1 is radiant floor in the basement, Climate Panel in about 70% of the main floor + 3 panel rads and 2 towel bar rads. The second floor is all panel rads. This house is 5,830 sq ft with lot's of glass to the South, 22' ceiling in the great room and 9' everywhere else including the fully finished basement. The load calc indicated 91,579 btu's at design and I sized the rads to hit the required output at 140* max, keeping the system condensing in all outdoor temps. The floor was figured for a max water temp of 95*. I set the both curves on the Vitodens to hit the target temps above at -10*. At this date, the curves we are working with are about 1/2 what I originally figured. The homeowner loves the fact that he's burned less than 500 gallons of LP since September but his wife is miffed that the floor runs so cool she can't really "feel" the heat. The rads run luke warm most of the time unless it gets near zero outside.

The insulation package was a little better than normal with blown 2x6 walls, wrapped outside with Low-E foil faced 1/4" foam and 3"x10" half log siding. I figured an r value of 21 for the walls, The ceiliing has from 14" (roof/ceiling combination) up to about 20" in the open attics.

Judging from a rough calculation of floor and rad output at the present water temps the heat load at design has to be in the 55-60,000 btus range.

The second house is the one I had the pics of five Vitodens hanging on the wall.( four of 'em run the driveway) It is now completely insulated and is maintaining 65-70* with no problem. The system was designed like the first with a max water temp of 140 at design. I have the basement floor running at 75-78* surface temp and have only 8 out of 22 radiators installed. The curves are 1.2 on the rads and .6 on the floor, a little higher than what they will wind up at but I figured with only 35-40% of the heat installed , I'd better run a little warmer water to keep the place heated. The heat loss calc on this one was 109,000 btu's and when I checked the house the other day at 2* above the Vitodens was barely off idle. Water temp was running 127*.

I'm not complaining in the least but I am curious as to why the load clacs seem to be consistently high for these combo hydronic systems. The F/A houses we do seem to be more in line with the calcs than the hydronic houses. Could there be that much difference in the ACH in the structure between the F/A system air flow as opposed to the slow, gentle air movement provided by a hydronic system? For those of you familiar with HVAC-Calc, I use the middle (average) selection for ACH on both F/A and Hydronic calcs.

What do you guys think?

Brad White_9

This is worth a study...

I cannot wait to see what Mike T. of Swampeast, MO adds to this discussion

Thinking along the lines of the Cd factor in energy estimating by the DD method, those kinds of factors. "No matter how tightly you calculate it, it gets cut by about 40 percent". Maybe the Vitodens' way of tracking/metering energy input is revealing what a heat loss really should be?

At first blush I would think that the infiltration would be the wild card variable. Improper return air as we all know can lead to "that giant sucking sound" in certain rooms and outflow in remote rooms with no return air pathway. That is a good hypothesis. What difference is made going from the average ACH rates? I test-ran HVAC-Calc a few years ago and settled on CHVAC by Elite Software in the end, but HVAC-Calc is very good at what it does.

Floor mass may be another but then you would only see that in the basement areas, so for now scratch that.

Internal gains? The second house you mention is not yet complete I gather so scratch that too.


I will just sit back on this one for now, but interesting it is.


Brad

S Ebels

Here's another thing

When the house was running on our temporary heating system, two furnaces providing 200,000 btu's, the construction guys in the house were griping about it being cold but the interior temp was 60-65*. When I was there last week one of them came up and asked to "turn down the heat, we don't need it 75 in here to work". Actual air temp was 67*! Granted, when the furnaces were running, the insulation was not complete, but the air temp was still in the low to mid 60's. What a difference a little radiant makes.

AFA air flow and the typical lack of return area goes.............we get very few F/A jobs because my estimates are without fail 10-20% higher priced than the contractor that does the majority of the work in this area. I always figure a minimum of 70 sq in of opening/duct size per ton with returns spaced appropriately throughout the house and in each bedroom. The low bid guy runs maybe 40-50" from what I've seen using a couple large returns in the main living area. Typical install for them would be 3 tons into an 8x20 duct system. So what I'm saying is that for our F/A installs, screaming returns are not the issue.

You may have a point on the Vito tracking the heating load accurately but that still wouldn't explain the apparent difference in the actual heat lost from the structure. No?

Then again...maybe it would. Instead of large shots of heated air blown intermittently into the house, the radiant system would provide constant even output. Have to ponder that some more..........got myself thinking now. I scare myself when that happens.

Brad White_40

Vito Tracking

I think we are grasping the essense of that concept. That the Vito is metering in the Btu's at the same rate that they are leaving more or less, but certainly more efficiently than FHA... it all goes to efficiency. The notion of bursts of heat intermittently versus purring sips of hot water coming back cool, how can one compare that?

Still, this may be a new era where empirical data trumps conventional wisdom/practice of calculating heat losses.

Good for you for taking the lead on FHA return paths by the way.

Brad

Mike T., Swampeast MO

Here's an interesting study

Note: Normal case for NEW construction has 22% duct leakage and system sized by Manual J.

A "good-resized" system has ducts well sealed (6% leakage) with heating system reduced by 25% for ductwork in unconditioned space and a whopping 50% for ductwork in conditioned space.

Comfort as good or better in the "good-resized" system with significant energy savings.


Another study (also from California) that I can't find right now arrived at the conclusion that Manual-J calculations [appear to have] a built-in "fudge factor" for "typical" forced air systems.

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

Here's an interesting quote from the linked document:

"For heating systems the simulations did not convert the equipment output energy into energy consumed because there was no explicit model of the heating equipment."

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

Methinks that the academic type need to be studying real-world systems like the ones you mention Steve. With these there IS an ability to ACCURATELY convert "equipment output energy" into "energy consumed"!!! With a decent sample with various shells, emitter methods and average supply temp requirements, some HIGHLY accurate models for determining true heat loss can be obtained.

My own crude model that predicts energy consumption in my house uses 80% of the computed HVAC-Calc loss (using "average" for ACH). Basement averages 50% above grade (100% to the north). Solid brick, uninsulated foundation with 7 doors including 2 garage doors and 4 fully glazed, 6 windows and I have allowed NOTHING for basement heat loss! Ground floor shell is still not complete but the heat loss is based on completion!

------------------------------------
The homeowner loves the fact that he's burned less than 500 gallons of LP since September but his wife is miffed that the floor runs so cool she can't really "feel" the heat. The rads run luke warm most of the time unless it gets near zero outside.

Can I ever understand that statement! The rads in my occupied space (kept about 63°F this season) only begin to get luke warm when the outside temp is low 20s or below! This currently works out to about 18¾ btu/hr/sqft at design conditions for a 1903 home with only reasonable insulation/infiltration control and extremely low occupancy load. Ground floor windows--MANY of them--are not yet weatherstripped and don't even have the interior stops or casings installed. There are aluminum storms. Only a few of the weight pockets are insulated. Fireplace damper is frozen in the open position.

S Ebels

Has anyone else

Has anyone else noticed anything similar to what I'm describing or am I an anomally?

Weezbo

i think....

the HVAC -Calc is more suited for forced air. i dont mean this in any derogatory way however i belive it "favors" heat calcs for F/A so that the purchaser will feel more inclined to go with forced air as the means for heat distribution....and secondary cooling.
try unusually tight buildings next hydronic run you make at it....

i lost a group of programs, that was one of them.

Mike T., Swampeast MO

Anyone Else

Unexpectedly low emitter temps with a radiant burner?

Constantin

Hi Steve...

... I used HVAC-Calc to come to my estimated heat gains and heat losses, but elected to substitute my own number for infiltration because I felt that foam-based insulation was going to yield better results than what Manual J, 7th Ed. was aiming for.

My contractor used Wrightsoft, which is based on the same Manual J tables. In other words, the results should have been (and were) similar, all things being equal.

I have to confess that I have not yet hooked up the boiler comepletely to the WEL, nor that I have run a test with DHW off to see how much the boiler fires within a given set of conditions. However, our fossil fuel consumption overall to date is less than 1/4 of what it was in our rental apartment, once you normalize on a per square foot basis.

Siggy's HDS calculated 900+ gallons of #2 a season, since September we have used less than 700. And we heat the water with it too. On the other hand, it has been a mild winter.

My overall impression of Manual-J, 7th Ed. is that they do account for "average" construction quality in both the shell and the heating/cooling system. When used properly (i.e. no padding, the published design-day temps) the results seem to be padded only a little bit. However, if you start substituting record-low temps for the ASHRAE 1% or 2.5% design-day temps, then a oversized system is likely to result.

Based on personal experience, this is where the biggest errors asre created. My contractor and I were very close in terms of heat loss, but over 2 tons apart on heat gain. The difference was explained by the design day temps used.

S Ebels

What are you thinking Mike?

The burner is one of the variables that I have been pondering also. Here's why. I have a nearly identical heat delivery system in my own home, consisting of Climate Panel and steel rads of various shapes, types and sizes. My boiler is a natural gas fired Vitola which tests from 85-88% combustion efficiency depending on water temp. My house is not new (1920's with two major additions) but it is wrapped pretty well. I'm a touch light on radiation but it's certainly more than the house we are working on in the above post.

Here's the thing that has me scratching my thinking itch. I have observed that my water temps run about 15-20* higher than the two Vitodens systems mentioned in order to provide comfirt. If (and that's a huge if) all other things are equal why is that the case?

The variable has to be the burner/control/boiler design so what's different about it? The biggest thing I can come up with is the fact that the Vito has the ability to EXACTLY match the water temp called for by the heating curve. Therefore, the temp in the system stays relatively constant. Constant temp from the rads/floor surfaces means there is virtually no variation in the output from those emitters with a modulator like the Vitodens. With my Vitola (with no mix valve) the heat output is affected by the variation in water temp between firing. Hence the boiler has to overshoot the target temp in order to find the average temp calculated by the control. Like I said above, the Vitodens can track the water temp right to the degree due to its design and a very accurate control.

The radiant burner in the Vitodens has to play a part in the equation also. It's just so different than a typical visible, exposed flame burner that the heat transfer would seemingly be different also.


GOOD GRIEF!! Why am I thinking about this stuff at 6:15 on a Saturday morning??!!! Maybe Kathy is right, IT IS A DISEASE!!!!

S Ebels

Hi Constantin

Good to know I'm not the only person thinking about heating early on a Saturday morning.

I agree 100% that the design temp greatly effects the calculated load. My confusion arises from the fact that the radiant houses we do seem to be over-radiated whereas the F/A houses seem about right using the same design parameters.

Brad White_40

12 Step Program

"My name is Brad, and I have a heating solution problem..

"I have gone for 12 minutes without thinking about heat. I was too weak the urge too strong...."

"One day at a time, Brad, one day at a time"

Mike T., Swampeast MO

What I'm Thinking...

...defies most explanation.

"The extremely low emissions achieved by the MatriX radiant burner are the result of the complete pre-mixing of gas and air as well as the low combustion temperature, which results from the large semi-circular reaction surface. A high proportion of the released energy is dissipated through infrared radiation from the reaction zone. This significantly reduces NOx formation."

"Over a gap length of only 36 mm, the hot gasses can be cooled [in a Inox Crossal heat exchanger] down from 900°C to only 50°C."

While I could be wrong, what I believe is acutally meant by "low combustion temperature" is low apparent combustion temperature. With a minimum of excess air, natural gas burns at around 2,000°C. BUT, such a temperature can never be measured directly via a physical object--instead it is measured by a spectroscope.

The "large semi-circular reaction area" would therefore [seem] to serve the purpose of reducing the apparent combustion temperature.

An aside on "flame". What is flame? What is fire? I've searched and searched and there is no "real" definition--only descriptions. Some physicists say the flame we see is a zone where plasma is converted into gas.

Plasma: "A plasma is an extremely hot gas that is composed of free-floating ions (atomic nuclei stripped of some electrons - making the ions positively charged) and free electrons (negatively charged). A plasma behaves much differently than a neutral gas, and is considered the fourth state of matter. A plasma conducts electrical currents."

I don't believe that anyone sees conventional flame on/around a MatriX burner. The "flame" just isn't right--it's not licking--it's just there...

If I put Viessmann's statements together with observation and physical nature, I seem to get this:

Plasma is widely dispersed in the "reaction zone". Because the plasma has been dispersed, the "flame" it produces is at a much cooler than normal temperature--say 900°C instead of 2,000°C. What happened to the difference? It was instantly transferred to the facing HX surfaces via infrared radiation. If these temperatures and Viessmann's statement of "high proportion" are anywhere near correct then somewhat more than half of the energy has already been transferred before the hot gasses ever reach the heat exchanger. A large amount of energy has passed directly from the plasma to the HX surface without first appearing in the flame. The burner acts like it's hotter than can be measured--even indirectly via a spectroscope. Thus the "low combustion temperature".

Did you notice another very important property of plasma? It is electrically conductive.

Here's where I'll get really bizarre. Just like the burner "seems" hotter than it is, I believe that some of this ability is transferred through the system to the emitters. The surface of the emitters has a tiny potential to act like the burner.

Make those emitters large enough and their average temperature low enough and you can actually measure the effect. The emitter temperature you can actually measure is lower than that required to liberate the heat transferred to the system.

I don't believe that this scenario breaks any known laws--it's just energy transfer occurring without all of the typical intermediate steps. Whether consequently or intentionally I believe this allows the Vitodens to transfer just the required amount of energy with previously unknown accuracy.

I realize this explanation is bizarre, but the alternatives seem less possibile. Standing iron radiators giving off 3°+ btu/hr/sqft/° of temp difference when that difference is very slight? Heat loss that's exceptionally lower than predicted when energy consumption is in line with the prediction?

Research physicists locked away in government weapons research labs are probably the only ones who would acknowledge that I'm on to something... Perhaps the Vitodens is a safe civilian application of particle beam weapon research. The timing is certainly right.

Mike T., Swampeast MO

Glad you can make it twelve minutes!

Mike T., Swampeast MO

By the way. The US Military now has a little-known sixth branch. (Fifth if you don't count the Coast Guard.) While I've heard it called by different names, the most common is "Space Command".

Collect a tiny bit of the boundless energy from the periphery of space and project a tiny portion of this such such that it appears as plasma somewhere else--like a missle in flight...

Why do you think the US military is completely re-organizing? Recall Reagan's promise that once developed, SDI technology would be demonstrated--if not shared? We seem to be able to act militarily with near impunity. Instead of defending against a collossus, we now seem to only need defend ourselves against relative barbarians...

I did not doubt Bush when he said that "amazing new technology" can reduce our need for oil by 75% in an extremely short period of time. I suspect that the real problem is determining a way to charge for it...

S Ebels

Ditto Mike

The first time I laid eyes on the Vitodens burner in the lab at Waterloo, I had a real "Holy Cow" moment. It was instantly apparent that this thing was way outside the parameters that you would say are normal, or typical when speaking of gas burners. I think that the infra-red, radiant or nonvisible heat creation occuring in the Vitodens combustion chamber is a key to the efficiency of the whole process of heat conversion and then transfer.

I think you are barking up the right tree when you note that the radiant heat emitted from the burner actually hits the heat exchanger before the actual heat from the "flame". It is heat that is not "contained" in the superheated air that we commonly call flame. It's pure radiant energy and as such has much more ability to transfer 100% of the "heat" to the target object, which of course, is the heat exchanger.

All of this gets no further in my mind than a hunch or a gut feeling because I have absolutely no training in physics or science other than what I observe and pick up along the way. In my mind however, what is happening with the Vitodens burner makes perfect sense based on observations in the field. There simply has to be something out of the ordinary going on in that boiler/heat exchanger combination. How else does one explain dropping the temperature from 1,700* to 120* or less in a distance of 1 1/2" while the flue gases are traveling at 45 miles per hour. If you think about in the ordinary context of flue gases conducting all the btu's it becomes obvious that this is seemingly impossible. The radiant portion of the heat transfer is the only thing that can possibly account for the btu's actually getting into the fluid.

This brings me back to the original question of why there seems to be a difference between the heat required for a F/A house as opposed to a radiant house. Could the same thing be happening, only on a less violent scale with the large, low temperature emitters found in a radiant system?

bob_50

Wait a minute

Steve and Mike, Steve you said in your original post the house seems to be over radiated, not over boilered. Compared to a forced air system I think the average MRT in a continiously circulating hydronic house would be higher. Therefore space temp can be lower for same comfort. The control system on the Viessmann is sophisticated enough to pick this up and lower the water temp below your ESTIMATED design water temperature to just exactly what is required. I think what you are seeing is the difference between a heat loss ESTIMATE and reality. I don't think that the water imbues the radiation with magical qualities because it comes out of a Viessmann boiler. bob

Mike T., Swampeast MO

Certainly agree that what I'm saying sounds bizarre if not downright kooky.

I've been measuring the temps of the same radiators in the same house for years. With no change save the boiler the radiators are significantly cooler. TRVs, constant circulation and a single circulator have been in use for six or seven years now. Vitodens for two. For the first year, Vitodens even operated at the same reset curve as the previous boiler. With the old boiler I could very accurately predict the temperature of given radiators in given weather with the TRVs maintaining temp for days or weeks and with rooms virtually undisturbed. For occupied space I could reasonably determine a reduced radiator temp to compensate for occupancy loading.

With the Vitodens and all other conditions the same the surface temp of the radiators is significantly cooler--always. As I mentioned, my overall fuel consumption is in line with a modified heat loss calculation--currently at 80% of HVAC-Calc. But, when I attempt to reconcile radiator temperature with output even very generous output estimates still don't find the rads warm enough to be producing even close to the amount of energy being consumed. The flue temp I measure shows that the boiler is operating at or near its' peak efficiency in most weather.

With outside temp in the mid-30s the highest temp I can find anywhere in the system is 72F. Occupied space maintained at about 61-65F depending on occupancy, sun, etc. The least oversized rad in the occupied space is 72F all the way across--the same temp I measure on the surface of pipe 3' from the boiler. The more oversized rads in occupied space are cooler--66 to 68F seems common. The rads in unoccupied space are stone cold--often at ambient or just a degree or two above. None are more than 60F. These aren't floors--they're just rather typically oversized standing iron radiators.

Remember that my experience in this regard is from one home only. Two different boilers (conventional atmospheric cast iron) and a Vitodens driving an otherwise identical system. In my case with essentially zero head loss in the piping and a fully TRVd system the Vitodens was truly "plug and play". Just pipe it in. The old boiler and circulator are still there but completely isolated. Four valves and two switches are all it takes to switch between them. I wanted to experiment with the old boiler this year but with gas so high I just couldn't bear operating the old gas hog for a week or so--such would quite literally have doubled my gas consumption for an entire month. Maybe next year if I'm willing to waste gas and money.

Mike T., Swampeast MO

My "training" amounts to high school physics, life-long curiousity, lots of reading and lots of direct observation.

I know your original question was about "heat loss" but it seemed to encompass the same problem I'm having as well--system temps lower than expected when a Vitodens is used as compared to boilers without that radiant burner.

Did you read that study I posted? One of the most interesting things I saw was that there was no model for relating heating equipment output to actual load--so they just used AFUE...

Modulating/condensing boilers do however seem to provide a basis for establishing this relationship with high accuracy. This will be especially true with proportional system--proportional either from very high mass like radiant floors or from proportional flow control via TRVs and emitters of reasonable volume with decent ability for radiant output. If someone with some $$$ would actually study such systems in the field, I believe we'd find out just how much Manual J heat losses are overstated. Of course some overstatement isn't really a bad thing--personal tastes change, extreme cold snaps happen, shells may well get more leaky over time, etc. The bad thing however is when you believe such a calculation is truly accurate and you add in a bit not knowing that there's already more than enough fudge factor to begin with!

I won't hold my breath for any such study in the US where forced air rules...

While I suspect that well installed, well adjusted and efficiently operated radiantly heated structures do loose somewhat less heat than an otherwise identical structure heated with forced air, I don't believe there's as much difference as you're thinking.

Add a condensing/modulating boiler into this equation and you get a big problem. Your personal experience, equipment ratings and heat loss calculations have all been based on inflated values--regardless of the system (air or water) NONE of the structures were loosing as much heat as you thought and NONE of the heating appliances were operating to the efficiency implied by AFUE.

The homes you're talking about aren't really loosing that much (or any) less heat than you think--the other homes are wasting more than you were led to believe.

If that condensing/modulating boiler happens to have a radiant burner, and if my (and it sounds like your) experiences are not unique, then there's another problem. Temps are too low--even compared to otherwise similar systems but without that radiant burner.

If (and I do mean if) this temperature anomoly is occurring it could make you think, "Why does the heat loss seem lower"? While the Vitodens is an awesome boiler, I don't believe it can actually reduce heat loss as such would imply that it's breaking some true law. What I do believe might happen however, is that some of the energy from the radiant burner passes trough the system, through the emitters and into the structure and its' contents in a form that cannot be measured as temperature by physical means.

p.s. The Viessmann paper titled "Condensing Technology" that I linked to here directly implies that the hot gasses from their radiant burner are 900C when they arrive at the HX surface. You can find the link under my post titled "Gold Mine".

Gordy

Radiant burner design

I do not mean to but in on this interesting discussion. I was up in tha attic rummaging around,and found my coleman heater. When I looked at the burner guess what the first thing that popped in to my mind was. Coleman was on to something, and did not even know it. This little heater kept me warm many a ice fishin days.

Gordy

S Ebels

Coleman heaters

An old Coleman catalytic heater that I have had for years was one of the first things that came into my mind when I saw the Vito burner lit up in the lab. I have used it for hunting, camping and fishing expeditions for nigh unto 20 years and it still works great. It's output has to be nearly 100% radiant as there is no visible flame, just this glowing orange ball. It's a pity their current furnace line isn't as high tech as their camping equipment is. I did do a combustion test on it once and the only thing I remember from it was that the heater produced copious amounts of CO. Definitely not for enclosed spaces.

Gordy

Uncanny

Low tech could be so high tech........Darn Germans anyhow!

Gordy

S Ebels

Checked the house again today

Outside air temp of 34*, indoor temp was 68*, tile guy working in blue jeans and bare back protesting the heat vehemently. Water temp to the rads at 110-112*, to the floor 72*. The heat loss calc has to be way high because we still have only 13 out of 22 rads hung. The 11-44 was obviously running just as low as it would go.........Has to be the calc......but then, back to original question, why is the same program so much more accurate when used with F/A. I always thought a btu was a btu and the method of heat didn't make much difference.

Brad White_42

Gotta Be

Radiant effect... wonder what else? Never mind "cold 70" you have "hot 68".

Wonder how the emitters weigh in against a FHA furnace, BTU for BTU?

There was another thread on Manual J where a writer opined that the tin knockers were putting stack ducts within the exterior walls and that you could read the structure through the melted snow on the roofs. Made sense that FHA practices could be accounted for to suit haphazard building practices... good a theory as any I have heard.

I would add that when ducts leak it is not nearly so dramatic as when water does.

Bob Sweet

I've noticed the same discrepencies

when running heat losses with respect to FA vs Radiant systems. Seems to me the Man. J software, with respect to FA shows a substantial part of it's losses in duct loss, most noticably when the ducts are located in an unconditioned space. Causing the radiant systems, designed with the same variables to be oversized. A more application specific software would be better suited for radiant systems.

Brad White_42

What surprises me about all of this

goes to the core of the basics.

Heat loss was always a function of "Area x u x Delta-T" for transmission and "CFM x 1.085 x Delta-T" for infiltration. (CFM however derived by ACH method, crack method or multiplier factors of course.) Nothing new there. Maybe "slab edge" and a variety of basement methods but the basics are generally accepted.

It would seem that somewhere within Manual J software -and the manual or 'by hand' basis-, there simply has to be a factor in there to account for this on air systems from what I am reading.

Given that "Area" is a user-input as well as Delta-T, presumably, then it has to be either a "u" factor skewing or an overall safety factor.

I use Elite CHVAC and like it. Not perfect, not always intuitive but once you are in a groove it is efficient.

What I like about Elite products is, the instruction manuals have all of the algorithms which their engine uses for a given program. Nothing is hidden. The algorithms are based on ASHRAE methods and uses both CLTD for heating and cooling and Radiant Time Series (RTS) for cooling as a toggle function.

Do the Manual J programs have such transparency?

Generally and typically, most codes require or at least recognize ASHRAE-basis caclulations as a reference standard by which energy use and plant sizing shall be derived.

What I do not like about CHVAC is that it assumes every system is an air system. There are no hydronic options. All systems are based on and are termed "air handlers". Arrgh.

In my office we use Carrier HAP (Hourly Analysis Program). I believe this is the evolved "E-20" program that Carrier used to have, or may be it's own developed product.

To me it is an energy modelling program that just happens to have a heat loss/gain function. But it does allow the user to select what type of system. This last part seems to be a function of the energy modelling portion, taking into account parasitic losses such as fans (all types and drives), or pumps, also of all types.

To my knowledge though, these programs give results in therms of heat loss/gain that are consistent.

On the other hand, this thread is bringing to the fore that any design really, truly needs to have follow-up in terms of actual load demand versus calculated. I do that occasionally, asking an owner a year or so into a buildings operation for a copy of their energy usage to compare. But this haphazard practice I think will become more routine from now on, thanks to threads like this.


Final thought on calculation software: For years before programs, my heat loss calculations were done on graph paper or ledger/analysis pads. Later in Excel or Lotus 1-2-3. No magic. Just a "Box in Space" emitting heat at a certain rate. Is anyone willing to take a job they did on Manual J and try it "by hand" for comparison?

When I have done so as a check, I get the same numbers compared to Elite CHVAC by the way. I mean, not much to it.

My $0.02 (Deflated over number of words

Brad

Plumdog_2

I thought the same thing

Coleman had a catalytic heater back in the sixties that had a dome on top. You lit it and after awhile the flame went down and it just glowed; or on very low settings it just felt warm.

Mike T., Swampeast MO

Obviously the boiler is modulating nicely. Have you clocked the meter to estimate input and verify that it actually is running "as low as it would go"? At 110-112°F boiler efficiency of about 93-94%? Then compare estimated output to heat loss calculation under the current indoor/outdoor conditions.

Since it sounds like you're there pretty regularly, why not start adjusting for an ideal curve? Perhaps take slope for the panel circuit down to 0.6 with a shift of 7°C and sun dial at 68°F? That will put the target at about 101°F in 34°F weather. Let the system stabilize for at least two days.

Might be too low right now, but when all the rest of the panels go in, it will probably be too high. If too cool only in colder weather increase slope--not shift.

Are you using a LLH? 11-44 can have up to a very generous 15.4 GPM before it's required. If the radiant areas have too much head loss to get the necessary (but still within limits) flow, was it possible to use a layout similar to System Layout 2 where an additional circulator is installed behind the mixing valve for the underfloor but without using the LLH? Or if underfloor takes flow requirement above 15.4 GPM was it possible to do a layout similar to System Layout 6 where the TRVd circuit stays directly connected and the underfloor isolated via the LLH? (Know these layouts are for the 6-24 and 8-32 but I was under the impression that the larger models without built-in circulator used a Viessmann supplied VS pump controlled by the boiler.)

D107

Should humidification be part of heat loss calc?

Since it seems to be common knowledge that, e.g. in the Northeast winter, a dwelling with a relative humidity of 40% or higher will FEEL warmer (and probably be healthier) than 20% at the same indoor temp, shouldn't that be considered? With higher humidity, a lower temp. can be tolerated, therefore less heat load.

David

DL_2

Heat Loss calculator - is it worth the time

I am a homeowner looking to replace my boiler. I was told by one person to do a heat loss analysis with the free calculator offered by this site. Another person told me that they didn't need one to know how large a boiler I would need. Who is correct?

Brad White_42

Unless the second person

is clairvoyant, I would try the free calculator.

Constantin

Yup...

... on the other hand, how close to the bleeding edge do you want to go? Having that 20%+ buffer on hand may be wasteful with the kind of clients that undertsand their heating system and essential for the kind that do not... you know, the kinds of customers who think that leaving a door open in the middle of winter or summer should not lead to any kind of comfort impediment inside the home.

One Gentleman I know insists that the way to cooling Nirvana consists of a window-shaker running full blast on one side of the room with a window fan exhausting/intaking on the other side. I think the problem would go away if he had to ride a stationary bike with a dynamo to power that madness.

S Ebels

Further adjustments

Mike, I was at the house again Friday. Outdoor temp was 20-22*, indoor was 71*. (Tile guy was still cussin' us out) We worked there all day after setting back the curve a couple points on the rads and 1 point on the floors. When we left water temp in the A curcuit was at 107 steady and B, for the floors was running 84*. Couldn't fell that the temp had dropped at all in the house. I have no shift dialed in on either circuit as yet, just getting a feel for how it's going to run. Every house is different and it's nice to be able to play with one for a while before handing over to the owners. We now have 13 of the panels installed which account for about 70% of the total system output.

Yes we are using a LLH. The radiant floor consists of 2 zones and the panel rads are on 3 different ones. Main manifolds are in two locations for both the fllors and the panels so head is quite a bit different between the 5 areas. I used a zone pump running through a Taco circ control panel for each of the 5 areas. These are called on by stats which act basically as a high limit for each area of the house. I'm shooting for the point at which the stat's will be calling for heat nearly all the time except when there a large influx of additional heat due to people, solar or cooking gains. The wall stats act a little faster than the TRV's and it gives the homeowner a familiar "user interface" to touch and control. (People that live i this type of house are usually into "control" if you know what I mean. If they can just play with the stat and push the buttons, it saves a lot of callbacks.

Also, there is no meter to clock. This system is running on LP gas. I'm assuming that the Vito was at minimum fire because it was running so low it was hard to hear and it would cycle off for about 3-5 minutes between the 6-8 minute burns.

Brad White_38

Infiltration Contribution

One aspect I forgot to mention came about when I was teaching heat loss calculation methods a few years ago. The thread of discussion was dominated by infiltration. I would have the students (architectural students at all levels) perform a heating and cooling load calculation on "their favorite room", such that each would retain a reference point all of their own.

For heat loss and in particular infiltration loads, I would have each student try the various methods and compare them on a hypothetical house. Crack method, air changes per hour method, CFM per SF of exposed wall surface method, all of those.

Out of that came the obvious question: What leaks into a room has to leak out of a room. Each room taken individually has it's own infiltration factor, as if it alone takes the brunt of cold air leaking in and exiting to other parts of the building.

Of course each room has to have this accounted for, because it will occur at one point or another. (No single room has diversity, the load for design has to be 100 percent.)

But what happens bulding-wide? Air can really leak in only on two sides plus maybe the roof at a given time. The other two sides and downstream side of a roof are the outflow points. The air that exits thus has to come, pre-heated, from the rooms that bore the brunt of the load.

What came out of it is that there is a lot of duplication in ifiltration factors when the sum of all spaces is taken together.

I will have to dig out my syllabus book and notes, but as I recall, we settled on taking the infiltration as a block load for the building rather than the sum of all room losses. Each room would be sized for 100% for radiation/air supply purposes but then backed out and applied as a building-wide total for boiler sizing. At the moment I cannot recall the factor and how it related, block to sum of peaks.

Just some thoughts.

Brad

Mike T., Swampeast MO

I've noticed that it takes at least one full solar cycle for curve changes to be apparent--slight changes (say just a degree or two of shift) take longer...

Did you notice if the boiler was cycling before you made changed the slope of the curves?

Do understand the t-stat "familiarity". If the homeowners are into "control" however, they should be able to figure out the Vitodens user interface.

As you surely know, TRVs are somewhat "relative". Relatively oversized rads seem to maintain a bit higher temp at the same TRV setting compared to less oversized rads. Have also noticed this year that supply temperature introduces some "relativity" as well. A significantly lower supply curve results in ALL of my TRVs maintaining slightly lower room temp for a given setting.

What's your calculated heat loss at 22° outside; 70° inside?

S Ebels

Yes, the boiler was cycling but at a longer interval, probably 15 minute burn then 8-10 minutes off.

Here's what I'm stumbling over on this system. HVAC Calc says the total heat loss for the house, including the garage, which is running same temp as the house, to be 71,493 btu's. This is at 70/22 conditions. There is no way on earth that the structure is taking that amount of heat to maintain 68-70*. There is also no way that the rads we have installed at this point can be providing anywhere close to that with water temps where they are. I doubt if the actual system output is hitting 50,000 btu's if that.

Something doesn't add up here and it almost has to be a large CYA factor on the calc.

Mike T., Swampeast MO

Those are Some Bizarre Results...

IF the boiler is indeed firing at minimum while producing "bursts" (burns longer than a few seconds but not hours of operation), then:

7 minutes off, 15 minutes on = 63% firing time = about 34.65 MBH consumed.

4 minutes off, 7 minutes on = 62% firing time = about 34.1 MBH consumed.

At the temps you describe, you're getting very good condensation and very high efficiency--not quite the max, but pretty close. Perhaps guess 96% or so?

Both are only about 45% of your calculated load at 96% efficiency!!!

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Since I don't have a low loss header can someone with the LLH and a natural gas boiler clock their meter to verify that the boiler does operate at minimum modulation during "bursts" when the indoor conditions have been maintained for at least a day or so?

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Did you also adjust the TRVs and thermostats for the radiant downward? Sounds to me like you're using all of the thermostats as a sort of high limit. If so, your boiler on-off estimates show something sort of interesting... See how the total burn time decreased only slightly when you reduced the curves? If you didn't adjust TRVs/thermostats down, then this makes a lot of sense--the curves are still adequate and you're getting a touch higher efficiency because the curves are now lower.

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

I presume no blower door test, correct? If not, what "estimate" are you using in HVAC-Calc? Do you have fully enclosed rooms? Since you don't have all the panels installed are the rooms without panels significantly cooler? If so, that would certainly account for some of your "missing" heat loss. Any way you missed or mis-estimated something in the heat loss calculation? Perhaps heavier than expected attic insulation? Either no recessed lights to unconditioned space ("heat suckers" as I call them) or if there, properly insulated with sealed, rigid boxes around them?

What brand panel (sorry if you already said)? Have you measured the temp of a panel or two and compared to boiler temp? (I've found the hand is VERY accurate when it comes to assessing delta-t across a panel or radiator.) You can often get a very good idea of the "adequacy" or the heat curve (when using TRVs) if you feel the pipe BEFORE the TRV and then feel the middle of the radiator. If significantly lower, then there's a good chance your curve has PLENTY of headroom that can be reduced if you're attempting to establish a base of bare adequacy.

If Buderus, the output ratings I'm seeing are fairly consistent with gross square feet of the panel. e.g. Model 11 is about 630 btu/hr per square foot at 180° panel in a 68° room.

Using their "conversion factor" for a 100° panel in a 70° room I get about 125 btu/hr for each square foot of panel. Would you perhaps want to tell me how many square feet of panel are currently installed and how many are planned? Tell me average temp of one panel in one closed off and fairly undisturbed room and your calculated heat loss for that room?

Sorry for so many questions. Your gap between consumed energy and expected loss [seems] so great that I'm grasping at some straws.

S Ebels

"At the temps you describe, you're getting very good condensation and very high efficiency--not quite the max, but pretty close. Perhaps guess 96% or so?"

Condensation is a steady stream not drips. I'd guess efficiency is in the 95%+ range also. Exhaust temp is less than supply water temp by 3-5 degrees.

"Did you also adjust the TRVs........" Trv's are still set just below 3. No change as I want to keep them open and find the point at which the room temp starts to drop significantly.

I presume no blower door test, correct? If not, what "estimate" are .......... No blower test is correct. I used the "best" infiltration factor for this house due to the dense pack cellulose in the 2x6 walls (some are 2x8) and good, but numerous, windows to the east, south and west. Lot's of can lights but they are buried under about 18" in the attic. No major factor there. I've been over my calc several times since I noticed this.........."anomally".........for lack of a better word.


What brand panel ........... Radson Integra panels, Vasco Lotus H2L1 series and Radson towel bars. No I haven't measured any skin temps on the panels but I can tell you that they are barely circulating because the bottom of the rad is much cooler than the top in most locations.

You have a good point in the missing heat being due to the fact that some ares of the house (though small) are a little cooler than the average temp for the whole structure.

Going back tommorow to start piping the drive manifold and if I have time I'll see if I can get some valid temps on the rads.

PS: Whatryadoin' Mike, writin' a book about this place??

Mike T., Swampeast MO

Thanks Steve. Am trying to see if we're experiencing the same "problem".

Not sure if you read my post yesterday titled "Heat Loss, Radiator Temps and Vitodens".

Gist is that my drywall finisher finally showed up and complained that the Eurocave was too cold. Turned up two TRVs slightly and significantly increased the sun dial setting.

Those two radiators (and the one in my office) are now the ONLY rads above ambient! If heat loss is estimate is anywhere near correct (and it's verified both by actual and predicted consumption) I'm getting right at 4 btu/hr/sq.ft. per degree of temp difference from iron rads!!! This at temps that "standard" tables say they have zero output!

Mike T., Swampeast MO

Have been searching for specs on those rads, but can't seem to find info for estimating output at other than "standard" temps. Am I missing something?