Blog Archives

Balanced Ventilation Brings in the Good Air, Banishes the Bad, and Conserves Energy

Posted by on 14/ 11/ 15

The best way to temper incoming air while reducing HVAC energy consumption is to use a heat-recovery ventilator (HRV) or an energy-recovery ventilator (ERV). These systems (see the drawing on the facing page) are balanced approaches that use the temperature and humidity of an exhaust-air stream (which otherwise would have been wasted) to temper the air of a supply stream, thereby reducing the HVAC energy cost. An HRV heats or cools incoming fresh air and can recapture up to 80% of the energy that would be lost without it. ERVs are better suited for hot, humid climates because they dry incoming air, thus reducing the work that the air conditioner has to do.

You Still Need to Clean Up

Ventilation is good at diluting gaseous com­pounds and small particles because small particles act like gase...

read more

Oedometer Test

Posted by on 14/ 11/ 15

The coefficient of permeability can be determined as a function of vertical strain in an oedometer test (see Fig. 3.9). The method is normally used for fine-grained (frictionless) soils to estimate their consolidation characteristics. The oedometer test is usually performed either as a constant stress or constant-rate-of-strain test. In a one-dimensional constant stress test a cylindrical specimen of soil enclosed in a stiff metal ring is subjected to a series of increasing static loads, while changes in thickness are recorded against time. The coefficient of permeability is given as:

 

(3.11)

 

K — cv ■ m v ■ Vw cv ■ m v ■ Pwg

 

where cv is the coefficient of consolidation, mv is the coefficient of volume com­pressibility, yw is the unit weight of water ...

read more

Falling Head Test

Posted by on 14/ 11/ 15

In the falling head test the head is a function of time during testing while water from a standpipe flows through the soil. The falling head test is preferably used for soils with low permeability, i. e. silty or clayey soils (see Fig. 3.8). For such soils the problem of excessively high hydraulic gradients (Fig. 3.7) is avoided as well as the practical issue that, otherwise, the head would fall too rapidly.

Equating the instantaneous flow due flow of water through the specimen accord­ing to Darcy’s law with the flow necessary for continuity gives:

Подпись: VПодпись: *Falling Head TestFig. 3.8 Falling head permeability test

h dh

q = K A = —a 4 L dt

 

(3.9)

 

where q is the flow rate (L3/T), h — h (t) is the head difference (L) at time t, L is the length of the specimen (L), and a and A are t...

read more

Stage 4

Posted by on 14/ 11/ 15

After examining the gradation curve in Figure 6.6, we can conclude that lower­ing the curve on the 8-mm sieve simply means a reduction in passing from 55 to 45%, which is an increase in the quantity of particles bigger than 8 mm from 45 to 55%. This move means that we should increase the content of 8/11.2 by 10%. This action should be balanced, so 10% has to be taken off the aggregate 5.6/8. As a result, the achieved composition of the mix is shown in Table 6.9 and the gradation curve in Figure 6.7.

TABLE 6.9

Example of the SMA Mix with an Uneven Distribution of the Coarse aggregate Fraction among Three Fractions— predominantly chippings 8/11.2 (example II, stage 4)

Подпись:component of aggregate mixture content, (m/m)

Filler 10%

Crushed sand 0/2 15%

Coarse aggregate 2/5.6 mm 5%

Coarse aggregat...

read more

@ WOOD FLOOR TRUSSES

Posted by on 14/ 11/ 15

@ WOOD FLOOR TRUSSES@ WOOD FLOOR TRUSSES@ WOOD FLOOR TRUSSES

Wood top and bottom chords are linked with steel tubing webs in the composite truss. The tubing is pressed flat at the ends and connected to the wood chords with a metal pin. Unlike wood trusses with metal plates (see 45A above), the webs of the com­posite truss are entirely free to rotate (on the pins) and therefore allow the truss to return to its original shape when the load is removed.

Composite trusses are generally more heavy duty than their all-wood cousins illustrated in 45A above. The largest composite trusses are capable of spanning
over 100 ft. They are made with double 2x chords, which sandwich the webs. The lightest-duty composite trusses are made with single 2×4 chords oriented flat and dadoed to receive the webs.

Like wood floor trusses, composite trusses easily accommodate...

read more

Mi Casa Es Su Asset

Posted by on 14/ 11/ 15

In his book, How Buildings Learn, Stuart Brand speaks of the difference be­tween "use value” and "market value”:

Economists dating back to Aristotle make a distinction between "use value” and "market value.” If you maximize use value, your home will steadily be­come more idiosyncratic and highly adapted over the years. Maximizing market value means becoming episodically more standard, stylish, and in – spectable in order to meet the imagined desires of a potential buyer. Seek­ing to be anybody’s house it becomes nobody’s5

On the surface, small dwellings may seem to afford greater utility than mar­ketability. These places are typically produced by people who are more con­cerned about how well a house performs as a home than how much it could sell for...

read more

Techniques CUTTING SQUARE WITHOUT A SQUARE

Posted by on 14/ 11/ 15

ONE OF THE MOST important skills a carpenter learns over the years is training and trusting his or her eye.

And one of the best ways to develop this capability is to cut square by eye. Instead of using a square to mark a 90-degree cutoff line on a board, simply make a quick pencil mark for length on the board, line up a circular saw, and make the cut. Over the course of framing a floor or a wall, this method can save you plenty of time.

If you’re comfortable using a circular saw, it’s not difficult to master this technique. Position the saw with the blade aligned on the cutoff mark and the front of the saw’s base parallel with the edge of the board. As you make the cut, keep the base parallel with the board’s edge...

read more

The earliest developments in Egypt, IIIrd millennium BC

Posted by on 14/ 11/ 15

One of the first depictions of an Egyptian king is found on a macehead,[92] where the king is apparently opening a breach in a dike with a hoe, next to a man who is filling a basket with dirt. This king, called the Scorpion King from the ideogram on the mace – head, is said to have lived around 3200 BC. This is the period during which writing first appeared in Egypt, and also a time of growing political unity between upper and lower Egypt.

Development of the capital Memphis

Herodotus visited Egypt in 460 BC when it was under Persian domination. He reports (on the basis of information from priests) that a king called Min (Menes) built the new capital of unified Egypt, called Memphis, at the border between the upper and lower
portions...

read more

Lognormal distribution

Posted by on 14/ 11/ 15

The lognormal distribution is a commonly used continuous distribution for posi­tively valued random variables. Lognormal random variables are closely related to normal random variables, by which a random variable X has a lognormal distribution if its logarithmic transform Y = ln(X) has a normal distribution with mean xln x and variance оЩx. From the central limit theorem, if a natural process can be thought of as a multiplicative product of a large number of an independent component processes, none dominating the others, the lognormal
distribution is a reasonable approximation for these natural processes. The PDF of a lognormal random variable is

ln( x) Mln x

Oln x

 

2

 
Lognormal distribution

for x > 0 (2.65)

 

Lognormal distribution

which can be derived from the normal PDF...

read more

TILE AND SLATE ROOFS

Posted by on 14/ 11/ 15

Tile and slate are relatively brittle, expensive, and easily damaged if you don’t know what you’re doing. And they’re slippery when wet. In most cases, hire a pro to make repairs.

Tile and slate are so durable that they often outlast the underlayment and fasteners. So when repairing or replacing these roofs, prolong the life of the installation by using heavy under – layment (30-lb. building paper or a self-adhering bituminous membrane), copper attachers, and copper flashing. Although these materials are expensive, if the roof lasts upward of 60 years without leaking, it’s money well spent.

Roof tiles weigh about three times as much as asphalt shingles...

read more