Efficiency vs. Economy

Ex Maine Doug

So you are

still young enough to celebrate those things??
And have you been a good boy all year?
Enjoy and eat dessert first!

[Deleted User]

My new system uses 8A for everything other than the boiler itself. For constant circulation - 8A X 120V = 960W. 960W for 1 hour = 960 watt hours. Consumption in WH X 24 hrs X 7 days X 52 weeks = 8,386,560 watt hours/year. Divide by 1000 for 8,386 KWH. 8,386 X $.1/KW hr (assumed cost of electricity) = $838/yr. This calculation is simplified in that it does not add the 7A drawn by the boiler while it is on nor does it deduct for the indirect DHW circulator (I don't have individual pump numbers right now). My system does not have a real large number of pumps compared to many pictures I have seen on the wall. The 10 cents/KWH is also not representative of actual electricity costs in many areas. Fill in your rate.

In the planned operation mode (not constant circulation) the system will use less actual power than many implementations because I do use a variable speed primary pump controlled by differential pressure rather than a fixed pump volume and a bypass. Short cycling will be managed with a buffer tank.

The numbers above are closer to leaving a 1KW portable electric heater running 24 X 7 rather than a light bulb. In "light bulbs" it would be 16 60W bulbs or almost 10 hundred watters. A reasonably well lit house and grounds. It is about 524 gallons of propane.

For system efficiency calculations it is not the simple heat recovery rate of the primary fuel as useful heat. It is the system. Controls, pumps, internals of the boiler, phantom loads from transformers and power supplies; everything. Obviously I have not read every post on the wall and other sites, but I have never seen anyone do system effeciency. Just talking about boiler heat recovery.

It seems to be "well known" that constant circulation improves comfort. I would be real interested is seeing a proper scientific study proving that to be true and quantifying the relative improvement in comfort so a cost per "comfort unit" can be assigned. Sort of like the "radiant heat saves money because people will turn the thermostat down".

Dismissing these numbers as irrelevant or the small cost of comfort strikes me as being very wrong. It is also a disservice to customers who have to pay for both primary fuel and electricity. They should be made aware of the costs and be a part of the decision on trade-offs controlling how the system will be used. Some users will not understand real well at first (and some will) but explaining is not that hard and should be part of the design process.

Mike T., Swampeast MO

Decreased Electric Consumption was a \"Bonus\" ...

...in new Vitodens system.

15 TRV "zones" plus 4 radiant zones.

Maximum electric consumption (single pump and boiler) approximately 100 watts. Typical consumption is 75 watts or less. (Circulator never runs at 100% capacity.) That works out to about 1.8 kwh/day.

Your boiler draws 7 amps @ 120 volts???? Unless you are in a true heating climate where heat is ALWAYS needed, surely it doesn't take the full 960 watts running 24-7 when you're just producing DHW...

Unknown

Yeah , the numbers don't add up

I cannot see a residential heating system drawing 8 amps on constant circulation . Are your numbers assuming EVERYTHING is running constantly ? When you are on constant circulation , wouldn't the only variable to the electric bill be the extra pump running ? And I thought that constant circ pump only runs if there is the need for heat , not all year long . I thought a typical pump draws about .7 amps ? How big is this system ? 7 amps for the boiler alone to run sounds high . Can you give us a little more info about your system ? What brand boiler , how many pumps , etc . Thanks .

S Ebels

Vitodens KW consumption

I checked a system that we installed last year just to see what the draw was with everything running.

We have an 8-32 pumping through a low loss header with 1 15-58 circulating 17 panel rads plus 5-200' loops of 1/2" suspended for floor warming. The 15-58 runs this all nicely on speed 2. 1 1/2" steel was used for the main piping going out to the manifolds which were reverse returned. The 1 1/2" was overkill but it dropped the system head to half what it would have been with 1".

Total current draw with the Vito burner and circ plus the 15-58 running was 2.18 amps or 261 watts measured with my Fluke digital ammeter. (digital has its place Mike) 261 watts =.261KW, .261 x $.0832 (our residential KW rate) equals $.0217 per hour or about $.52 a day to operate.
That's $15.60 per month assumming both pups and the burner operate continuously.

[Deleted User]

Partially right

> I cannot see a residential heating system drawing

> 8 amps on constant circulation . Are your numbers

> assuming EVERYTHING is running constantly ? When

> you are on constant circulation , wouldn't the

> only variable to the electric bill be the extra

> pump running ? And I thought that constant circ

> pump only runs if there is the need for heat ,

> not all year long . I thought a typical pump

> draws about .7 amps ? How big is this system ? 7

> amps for the boiler alone to run sounds high .

> Can you give us a little more info about your

> system ? What brand boiler , how many pumps , etc

> . Thanks .

[Deleted User]

Partially right

As I noted, my numbers do not include the boiler and does include the DHW pump which should not be included but as I explained - I don't have the individual numbers. Power consumption was provided by the contractor to determine maximum steady-state backup power requirements. Which is why I don't have individual numbers.

It is my understanding that constant circulation means that all the in-floor pipes have flow while boiler input is modulated in some way (on/off, variable). This implies that the primary supply pump is also running to support the pumped loops.

The point about the boiler and system being off part of the year is valid. I did not factor that into the arithmetic. Lost sight of that. I am in the Pacific NW and it does stay rather cool in the evenings, but the system would most likely be off for 6 months. Therefore the annual costs would be halved. For the 6 months of operation the monthly electric bill would still be equivalent to running all those 60 or 100 W bulbs or the electric heater. That was an hour by hour number. Annual cost and saved propane would be half what I calculated.

I will check back with the contractor and see if there might be a misunderstanding on steady-state consumption.

Constantin

The Vitodens electrical consumption is very low...

... I saw a chart at ACEEE recently and was floored by the the differences in electrical consumption of very thermally-efficient boilers. Here are the annual electrical needs of some boilers in the same kBTU range:

• Burnham Opus: 326 kWh (!!!)
• Burnham Revolution: 314 kWh
• Weil-Mc Ultra: 139kWh
• Viessmann Vitodens: 48kWh

I wish more folks would look at the electrical loads in addition to the thermal efficiency. After all, even though electrical energy is cheap now, it may not be in the future. Plus, if you're living off-grid, the electrical implications are quite important. Lastly, if a boiler lasts 20 years, as I believe a Vitodens will, then 20 years of $50 a year less in electrical consumption starts to add up.

psd_3

A Taco 007 circulator is rated at .7 amps (about equivalent to a 100W light bulb). Most homes would have 2 or 3 of these for their independent zoning, although fewer are possible with zone control valves. You could pretty much ignore the other stuff, which would be common to both constant and non-constant circulation.

Unknown

I still think the electric usage numbers are high

I'm by no means an electrical expert . And I still have not installed a constant circulation system , but am planning to in my own home . When you have a constant circ system running , is it going 24/7 , or only when the house needs some heat ? Do thermostats control the individual zones and an outdoor reset control the temp of the boiler ?

Also , I know you said you left the boiler power out of the figures . I thought the 7 amps is a real high number . We use Riello oil burners that draw maybe 3 amps tops . You said the system is propane . What else make the amp draw so high on that type of boiler ?

Unknown

What do they base the usage numbers on ?

I take it constant circulation is not a factor with these numbers ? Are they based on burner usage alone ? Still , there's a huge difference between the Viessmann and the Opus .

S Ebels

So True!

This is so true and so basic that it goes without saying. It makes no sense to put a 95% appliance in a 50% efficient envelope.

Tightening up the structure should ALWAYS be done first.

Dale

Other issue

The other thing is that motors like to run and waste elect starting up, IF sized correctly you want to see heating or AC system run constantly at design conditions. The hardest sell on this is AC where most people think that if their 1 1/2 ton outdoor unit is running all the time at 95 degrees that it's costing them more than the neighbors 3 ton that's cycling on and off. Modern variable input is the most effecient but the example is simpler for me with the ON or Off old technology.

PJO_5

Worth Mentioning...

After insulation, the next step - especially in the planning stage - is whether you can involve any "free" heat from mother nature. Passive solar is easily done in many parts of the country with some thinking beforehand...talk about the ultimate efficiency of the boiler not running.

The comfort issue is probably the biggest factor as Mike T first mentioned. Here's my take;

Everyone here says how perfect the modulating systems are in matching the load and I agree, but if a person is willing to "forgive" a few degrees up and down through the day - like mother nature does - then does that also add to the total system efficiency?

If the answer is "yes" (people willing to vary a few degrees) then setback works very well. If the answer is "no" then it doesn't work well at all.

Combine the adjustment of a few degrees of variance into the comfort situation with passive solar (and better yet, add active solar) and you have much higher total system efficiency, do you not?

Example; two floor house with simple zones top and bottom. While the people sleep upstairs the bottom floor is setback, and the top floor is comfortable. During the day (until the evening) the second floor is setback with the first floor at the comfort target. This is pretty typical, right? The boiler does the most work in the early morning hours in this type of home betweeen bringing the first floor up to temperature as the occupants awake and get showers, etc. so let's say the boiler is running at or close to design efficiency - modulating or not.

After the morning routine is done, especially if the house is unoccupied for the day...why keep the boiler firing - modulating or not - if you have good passive solar available? On the coldest days the sun is usually brightest...so let it in...and the house will overshoot the "target" temperature by a few degrees. Then in the late afternoon the sun's gift is gone, and if you have high mass the residual will stay for a few hours. This entire time the boiler has not fired - BEST efficiency!

By 7 or 8 that night, the temperature is getting down near the "target" again, so with a little experience you can get the boiler and delivery system going again...lower efficiency for the first few minutes, and then it reaches it's best efficiency.

If you have active solar, you have spent the equivilant of a couple of extra Vitodens up front, but if it's right you will NEVER pay for fuel...again, isn't that the best total system efficiency? If you have good passive solar, you will save substantially in fuel, no matter what boiler you have without the huge up front cost...isn't that very good total system efficiency?

I only know this from my area of SE Pa. where solar is pretty good, but my own house does this very well. I am doing a design for a friend building a home, and he wants to copy mine - except for one of the companies I used for some supplies (we've beat that to death here) :-)
He came to my house without calling first on Friday night, and it was 8:30 p.m. and the temperaute was 72 degrees (on target) on the first floor. He wanted to walk on my radiant floors and asked why they didn't feel warm...I said because the boiler hadn't ran since that morning. He was disappointed in not getting to "examine" the floors but also very surprised the boiler hadn't ran all day. His homw will be the same way as far as passive solar, so that made him happy.

When I got home at 4:30 that day the house was 75 degrees in the same area, and there is the "forgiving" of a varying temperature I mentioned.

As far as constant circulation, I have five circulators total for my six zone system w/ primary secondary piping so I only use constant circulation for the radiant system when I get near design loads - like right now (the wind chill was -12 this morning). The shoulder seasons, I run the pumps for a few hours a day at most, and use setback substantially.

IMHO it is this mix, combined with the passive solar (no active - yet) and the willingness to go a few degrees above and below the target that makes my total system efficiency pretty high.

What do you guys think?

Thanks for bearing with me on this long post...

Take care, PJO

Mike T., Swampeast MO

Couldn't agree more that good passive solar design is wonderful--it doesn't cost too much, has zero maintenance and really is the only "free" heat. There might be some comfort concession, but with some active means to move or block excess heat such can be kept to a minimum.

Main problem with passive solar is that it's not suitable to all building lots/home styles and is difficult to integrate into existing, older structures.

May try some active solar if I can afford the $$$ in a few years. Sent a rather odd design to Viessmann America that integrates solar into both space and domestic hot water heating. Only a small additional circulator for the solar portion and little in the way of additional controls/devices. Unfortunately, it requires a connection to the Vitodens brain that's not available. Maybe someone there will experiment and the control will appear

Combined the space/DHW heating for much the same reasons you mention Patrick. Peak DHW loads rarely occur during peak solar collection times in my lifestyle. But, minimum space heating demand occurs simultaneously with peak solar availability. Idea is to move the solar energy to whichever system requires the lower supply temperature at any given time. In my system at least, that will typically be the space heating system during the winter. Other than the needed control, only other problem is economic--solar portion will have relatively high return temp so those expensive evacuated tube collectors are needed for best collection efficiency.

dircom

Mean Radiant Temperature - Comfort

We all know just because two buildings might have the same air temp, that comfort is not neccesarily equal.
We are not buying Heat per se, but are really buying comfort, ideally at the lowest total cost of ownership, with the least damage to the environment.
Is the biggest factor in comfort Mean Radiant Temperature?
My bed is next to a 65 year old lathe and plaster wall. The air temp might be 70, but the wall feels cold.

If I put a heating pad in bed to warm my cold feet, that makes me comfortable, If the heating pad is on the floor it doesn't make me comfortable. The heating pad is still putting out the same BTU's. If you put the heating pad back in the bed during the day, and cover it with a comforter, where is that heat going? Isn't some of it being held like in a thermos bottle?

With staple up radiant heat do some of those Btu's migrate through the subfloor to the plate and out. Some energy stays between the floors on a two story building warming the space, Is the energy between the floors unavailable/wasted ?

If you put a high temp radiator on an outside wall, you lose more heat than on an inside wall -right?

Would the ideal comfort be, radiant floors, walls and ceiling? Would your body have fewer radiant losses?

If you have a radiant ceiling does the energy get radiated in all directions and warm the walls as well as the floor, furniture, people etc?

Unknown

Just guessing at how the tested pressure would translate into actual infiltration under wild conditions, guessing a low pitch roof, guessing no marshy soil or ledge underneath, then I'd feel comfortable with anything capable of 60kBTUs output minimum in that scenario.



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