BIN method and Degree Day

[wufi2004]

Who can tell me what's the difference between BIN method and degree day? What's the cons and pros for each of them? Thanks!

I know sth, but i cannot find what;s the good point and limitation for each of them.

 

[1HVACEngineer]

DEGREE DAY METHOD
Degree Day concept was first developed to compare indoor comfort conditions to outdoor temperatures. For example, Heating Degree Day (HDD) with a Base Temperature of 65°F; assumes that whenever the outdoor temperature drops below 65°F you will require heating. Typically, HDD’s are published on charts; listed by location at various base temperatures. Once you have the correct HDD for your location and base temperature, you can estimate the yearly heating energy usage.

A drawback for HDD is that it assumes all days of each month are identical. Additionally this method does not allow for climate changes from year to year. The benefit of this method is that you can preliminarily size equipment with minimal calculations. Think of it similar to a macro analysis method, advantages for early design purposes.

BIN METHOD
Bin Method is developed from historical weather data for a particular location. Calculations may be performed using weather bins, which are created by recording all hourly occurrences of closely related weather as if they were identical. Hours that fall into a certain range of some parameter, most often dry bulb temperature are collected, and then distinguished by the mid-point of the range. The way to deal with other parameters is to calculate the average value of all of these parameters in each individual bin, which it referred to as the "mean coincident" value. That average value is then used for energy calculations.

A drawback for Bin Method is that it assumes that all hours in each bin have the same “mean coincident” conditions. Additionally, because the average dry bulb values are used for calculations purposes, the extreme high and low conditions may be excluded from your calculations. The benefit of this method is that you can fine tune the selection and sizing of equipment. Think of it similar to a micro analysis method, advantages for detail design purposes.

 

[friartuck]

The degree day method is based (in the Uk ) on a base temperature of 15.5 degrees. It is assumed that if the external temp is at 15.50 degrees, then heating willnot be required. (there are actually corrections which can vary this figure but I need a few pages more to explain)

Now if you have a day that has an average external temp of 14.5 degrees, this is ONE DEGREE DAY. Subsequently, if you have three days at an average of say 12 degrees C, then each of those three days will give you 3.50 degree days so the total degree days for thos3 days will be 10.50 DD's. (phew---understand the concept)

Note: that for a cold day i.e. -1 degrees in the Uk, then the max DD will be 16.50 per worst day

Now it can be worked out from historical date (by the Met Office)what the actuall DD's are for a year or a month or a week etc in any area. For my area, it is (i think I remember anyway) about 1800 DD's (Ish)

You can use this info to relate the 20 year average with an actual year and also you can use it to work out an average running cost.

For simple calculations, (and I mean really simple...and not particularly accurate or meanigful) then you can compare the area DD's with the maximum DD's (i.e. assuming that for a 9 month heating season (in the UK Sept to May) we can calculate the max DD's and use the ratio of the actual to the max to assess the load factor.

Let me expalin again:

Max DD's for a typical 39 week htg season at 5 days per week is 39x5x16.5=3918

actual DD's (measured by met office) for whre I live is say 1800

so load factor is 1800/3918=0.45 (LF)

this in laymans terms means that very approximately for this period, the heating would be on for an average of 45% of the time at full load or at 45% of the load for all year running (if that seems logical)

There are a number of corrections for controls, intermittency, building weight etc.

see CIBSE Guide Book B

PS

haven't got a clue what BIN method is



Friar Tuck of Sherwood

 

[briand2]

Friar Tuck,

Please find below a link to a table containing a reference to the bin method (via the CIBSE web site):

http://www.cibse.org/docs/bsertindtable.doc

As far as I can tell, from BSRIA / CIBSE / BRE documents I've seen over the last few years, the "bin method" is just a sampling procedure similar to a histogram; give it a new name and maybe it sounds like a modern invention!

Regards,

Brian