Cli-mate CLI-AP30 Spezifikationen PDF herunterladen (Seite 19)

Flow Rate per 30 tubes

Temp Rise @ 150Btu/ft

(Clear Winter Day)

Temp Rise @ 320Btu/ft

(Clear Summer Day)

1 gpm (3.8 Lpm)

F (3.3

F (7

3.6. Stagnation and Overheating

3.6.1. What is Stagnation?

a) Stagnation: Stagnation refers to the condition that occurs whenever the pump stops running. This could

be due to pump failure, power outage or most commonly, as the result of a max tank temperature protection

feature setting on the controller. During stagnation, the collector, unable to actively dump heat, will continue

to rise in temperature until the heat loss from the collector and piping equals the heat being absorbed. In

strong sunlight with high ambient temperatures, the collector will reach a peak stagnation temperatures of

about 428

F (220

C), if dry (decommissioned system or drain-back), and a lower level of 320

F (160

C), if

the piping and collectors contain fluid (as in pressurized systems).

b) Consider High Temperatures: Components that may be exposed to the high temperatures such as

valves, plumbing or insulation should be suitably rated. Heat will not migrate downward to the tank because

heat rises. But when the pump turns ON, a batch of super-heated water may be delivered to the tank.

Although that will only last a minute or so, it should be considered when sourcing materials for the piping on

the return line to tank.

3.6.2. System Pressure & Boiling Temperature

a) Boiling Temperatures: The boiling temperature of water (or other fluid) is directly related to the pressure

of the system. Water will boil at a higher temperature, the more pressure it under. This is a very important

concept, as the pressure of the system can greatly influence the operation and reliability. Generally, a higher

pressure is better (within reasonable limits).

The table below provides pressures and corresponding boiling temperatures for water. These will be

slightly higher for 50/50% glycol mixes, which on average have a boiling point of 220

F (104

C) at sea level

(i.e.1 atmosphere of pressure) versus pure water at 212°F (100°C).

PRESSURE and H

O BOILING POINT

PRESSURE and H

O BOILING POINT

PRESSURE and H

O BOILING POINT

PRESSURE and H

O BOILING POINT

PSI

kPa

14.5

212

101

100

247

203

120

43.5

271

304

133

289

405

143

72.5

304

507

151

317

608

158

b) Different Fluids: In a closed loop system using a heat transfer fluid, the properties will be different than

plain water. The boiling point of all heat transfer fluids used in Apricus OG-300 systems have a boiling point

higher than the temperatures reached during stagnation. See Appendices 10-17 for individual specifications.

c) Pressure Loss with Height: Even though a system might be a closed loop and pressurized, there is

always some pressure loss caused by height. This is extremely important to understand when deciding the

system pressure. The loss of pressure is about 0.5 psi per vertical foot. This means that while the pressure

at the pump station may be 40 psi, a vertical rise of 50 ft. will result in only 14.5 psi at the collector, which is

the same as atmospheric pressure. A low system pressure can result in bubbles (vapor) forming within the

heat transfer fluid due to a lowered fluid boiling temperature. These bubbles will collect in the high points in

the solar loop piping, especially within the collector itself and can result in air locks that the pump may not

be able to overcome, resulting in no flow and then stagnation.

Apricus Solar Collector Installation & Operation Manual - USA

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