Sharp JX-9400 Informazioni Techniche Scaricare il pdf (Pagina 45)

gas conservation equations can be rearranged so as to obtain one system of

equations per node, giving all airﬂow rates entering in this node. At steady

state

I

j ¼0

½C

 C

Q

ð2:6Þ

where:

is the injection rate of tracer gas k in (or just upwind of ) node i,

is the concentration of tracer gas k in (or just downwind of ) node j,

is the airﬂow rate from node j to node i.

‘Just upwind’ and ‘just downwind’ mean far enough from the node to ensure a

good mixing, but close enough to have no branching between the injection port

or sampling location and the node.

Each system can be rewritten in a matrix form:

¼ C

ð2:7Þ

where:

is the vector containing the tracer gas injection rate in the zone i,

is the matrix containing the concentrations diﬀerences, C

 C

, of tracer

k between zones j and i,

is the vector of airﬂow rates entering into zone i from zones j.

Airﬂow rates leaving the zones are determined by mass conservation equations

j ¼0

½1  

Q



j ¼1

½1  

Q

ð2:8Þ

An application to a typical air handling unit is presented below.

General method for ‘black box’ air handling unit

In most cases, it is not practical to inject tracer gases and to sample the air

within the air handling unit. It is often much easier to ﬁnd (or to bore) small

holes in duct walls to insert the injection and sampling tubes. Therefore, a

method for assessing airﬂow rates in air handling units using injection and

sampling ports located only outside the units is presented below.

Building the system of equations

The ducts, leakage and shortcut network in the air handling system seen from

outside, like a black box, are represented schematically in Figure 2.8.

Recirculation may be on purpose, or could result from leakage such as

that sometimes found in heat excha ngers. It occurs anyway between nodes 6

and 2. Regarding indoor air quality, there is no diﬀerence whether the

24 Ventilation and Airﬂow in Buildings

1 2 ... 40 41 42 43 44 45 46 47 48 49 50 ... 210 211

Commenti su questo manuale

Nessun commento

Sharp JX-9400 Informazioni Techniche Pagina 45

Commenti su questo manuale

Prodotti e manuali riguardandi Stampa e scansione Sharp JX-9400