Heating degree days again

Rick_41

Ok, very interesting but you say that windchill is not much of a factor? Doesn't the outside of a building and esp the windows respond to loosing heat via windchill? I understand about how not heat producing things are not effected by wind chill after they lose what heat they have and that 10 degrees of real ambient temps a rock will only get to 10 degrees and no colder despite high winds. But isn't it true that the rock if the day has been warmer will go down to 10 degrees a lot quicker with wind chill?
So in a building the heat eventually finds its way outside that vessel. Doesn't pulling heat away from the exterior walls and winds work to cool the building down faster?
(not counting for infiltration losses due to)

Also, here we are at more than a third of the heating degree days of a normal season gone. I have several buildings in which I pay for heat. On none have I spent 1/3 of my normal oil usage this year. In this mild weather it seems that despite the numbers of the heating degree days these places just are not using the oil as the same numbers of the past years .

Rick_41

Heating degree days again

OK I think I understand better about heating degree days but for real use of how the weather effects MOST buildings, wouldn't simple gizmo used as a standard be more effective?
IE a 1/4 inch aluminium welded box that is set on in a no shade area that is painted with flat black rustoleum type paint with a light bulb of a certain wattage (to make it easier to use/replace than a heater) and a sensitive thermostat and wattage meter. Thus it would record solar gain (maybe an orb would be better for that) an effective windchill loss, and just regular heat loss. This should be pretty accurate in measuring the electrical use keeping the unit at temperature.
Maybe there is something like that already (?)
As far as the cal of heating degree days, the windchill and solar not coming into play, What happens if in the 24 hours if a cold/warm front causes a warm/cold hour or two and then the rest of the day is very different. On that given day it would seem to me that the HDD information would be very inaccurate.

Brad White

Weezbo, is that you in there??

The Degree-Day method is surprisingly accurate and is affected (skewed) by very tight buildings, higher internal gains from lights & electronics and heavier than normal insolation.

An hour or two of warmer or colder weather will not affect the Degree-Days very much. Properly measured, the temperatures are measured every hour and taken at 1/24th of the day. Thus any hour of unusual weather is not overly weighted against the entire day. The mean for the day is extracted and is subtracted from 65 degrees as the base.

(A 50 degree base is commonly used for commercial and institutional buildings with greater area to envelope ratios and higher constant internal gains.)

All Degree-Day gross results are multiplied by the Cd factor which helps correct for normal insolation and internal gains. This factor averages about 0.60 for the 6,000 DD range but can be anywhere between 0.4 and 0.7 for areas where heating is of concern. The very warm and very cold climates are closer to "net".

Forget "wind chill" because that is a physiological effect on a body that perspires. Wind will affect infiltration certainly but is not constant. Most heat loss calculations assume infiltration rates based on a 15 MPH wind. Many calm crisp cold days will negate the occassional windy day.

John@Reliable_14

Brad, (Weezbo) you very funny...................

question also reminds me of a great old song "I got to much time on my hands"

chapchap70_2

> OK I think I understand better about heating

> degree days but for real use of how the weather

> effects MOST buildings, wouldn't simple gizmo

> used as a standard be more effective? IE a 1/4

> inch aluminium welded box that is set on in a no

> shade area that is painted with flat black

> rustoleum type paint with a light bulb of a

> certain wattage (to make it easier to use/replace

> than a heater) and a sensitive thermostat and

> wattage meter. Thus it would record solar gain

> (maybe an orb would be better for that) an

> effective windchill loss, and just regular heat

> loss. This should be pretty accurate in measuring

> the electrical use keeping the unit at

> temperature. Maybe there is something like that

> already (?) As far as the cal of heating degree

> days, the windchill and solar not coming into

> play, What happens if in the 24 hours if a

> cold/warm front causes a warm/cold hour or two

> and then the rest of the day is very different.

> On that given day it would seem to me that the

> HDD information would be very inaccurate.



http://www.johnsondegreeday.com/howorks.htm

chapchap70_2

http://www.johnsondegreeday.com/howorks.htm

Weezbo

Huh? *~/:)

It is with considerable consternation and under severe duress i scribe this to the electronic page...

It is 24 below zero , i have about 134K rolling through 18K of radiant and only dummy bypasses.....and you wann me ta do WHat?

it would be ok if:(1) it were a condensing boiler

(2) had a heat exchanger that was made out of rubber:))

(3)didn't have an inspection Tuesday morning .

(4)the Vitolas arriving Thursday..

(5)the VV VS whenever the factory makes me a couple...:)

and some inclination that i oughten be thinking of going back over there tonight to readjust the 1 1/2' MAIN Bypass )

ok,,,there is a real good read on BINS and Heating Degree Days that i will look around in my computer to find for you. You will like it. it is simple easy read.. it has a chart for just about everywhere on the planet, In COLOUR! with all the sniveling clauses firmly in place:)

it also has the choice of fuel and a readout of your general area which you can adjudicate to your specific Degree and azimuth and topographical area and surroundings

Habby New Years ,

oh. until then try Taco system Analysis tool...i think it is free at Taco.

Brad. Thanks for the kind thoughts...oh! there is something of a slight disclaimer to the DD windy day theory......like the guy said,

"i feel really bad about sleeping with my third cousin"

so his buddy says "wellll. quit counting"

Brad White_9

Windchill

Windchill as a meterological term has to do with the affects of wind on the skin, specifically perspiration (always present) and the evaporative effect that has on the skin. Thus a windy winter day feels colder than a still winter day. If your building had sweat glands, I would worry. Not just about windchill either.

Buildings are affected by wind principally as a function of increasing infiltration, the gradient of windward-side pressure, leeward side pressure and the height (stack effect) all contribute. More wind, more infiltration, simply. Now, because your base infiltration is taken usually at a 15 MPH base, we know that is not a constant. Sometimes more, more often less, depending on where you are.

As for other affects in inanimate objects, your rock, windows, house, etc., the only effect that wind has is by increasing convection.

Now, your wall U value is figured using inversed R values which include, "just for showing up", an R value of 0.68 for the inside wall still air film and 0.17 for the outside air film... That 0.17 already has been taken at a 15 MPH wind. Suppose it was a 50 mile an hour wind and it went to zero? All you have lost is an R value of 0.17... Yawn.

True, you cannot cool a (dry) rock below ambient with high winds. But if you wet the rock (with water, not used beer thank you!), the rock or whatever you are ------g on, will cool below ambient due to evaporation. The ancient Egyptians made primitive ice this way by dampened palm fronds in dry desert night air. Mixed with fruit from the Negev Desert and you have the makings of world peace.

So the key to minimizing convection is good insulation so that your conduction does not get the heat to the exterior very well.

Keep your walls dry and don't try the rock experiment on a public way in daylight.

Does that make sense?

Brad

Mike T., Swampeast MO

While degree days don't account for additional loss due to wind (mainly increased infiltration), neither do they account for gains from sun, appliances, lighting, people, etc.

While the additional loss due to higher wind is relative to outside temperature (infiltrating air gets colder as the outside temp falls), the additional gains are mainly independent of outside temperature.

In other words the unaccounted gains make up a greater proportion of heat loss as the weather is increasingly mild. This is likely why your oil usage isn't "tracking" well simply via degree days when you're comparing to "average" weather in years past.

Rick_41

Wow thanks guys, I need to read this a few times as its out out my field but its a great education,and Thank you all for being patient. Explaining this is probably like trying to talk Swahili to someone from China. A bit exasperating if someone is out of the loop of understanding basic stuff.