lp-364 Rev. 000 Rel. 007 Date 2.12.18
8
E. Delta-T Controller Settings
Usually a Delta-T ON value of 8 – 20
o
F and Delta-T OFF value of 4 -
10
o
F is appropriate. These settings may need to be altered slightly
according to location and system design. Refer to the instruction
manual provided with the chosen solar controller for appropriate
settings.
F. Stagnation and Overheating
Stagnation refers to the condition that occurs when the pump stops
running. This can be due to pump failure, power blackout, or as a result
of a high tank temperature protection feature built into the controller
which turns the pump off.
If the system is designed to allow stagnation as a means of preventing
tank overheating, the collector and plumbing in close proximity may
reach temperatures greater than 395
o
F; components that may be
exposed to these high temperatures, such as valves, plumbing, or
insulation, should be suitably rated.
If the system is designed to allow stagnation of the collector when the
tank reaches a set maximum level, steam may form in the collector(s).
In such a system, temperature relief valves or auto air vents should
be isolated (using an isolation valve) on the collector outlet, as these
options may not be able to withstand the high temperatures and allow
stable stagnation of the collector (may dump hot water).
In the event of component failure or extreme conditions, the PTRV on
the hot water storage tank may open as a safety measure. Under such
conditions, the collector will normally reach a maximum temperature
of around 395
o
F. Any heat returning from the collector is generally
not enough to cause a continued increase in tank temperatures (e.g.
heat input is less than tank heat losses), and therefore is able to meet
requirements in some regions limiting hot water dumping. A crackling
noise may be heard coming from the supply line when hot water is
used as the pressure in the system drops and steam forms. This is
normal.
G. Sizing System to Avoid Overheating
The system should be sized so that overheating of the tank is difficult
to achieve in a single day, even during hot, sunny periods. If the system
is oversized, such that excessive heat is often produced during summer
months, consider installing a drain back system, a heat dissipater
unit, and carefully review the points in Part 3, Section H, Preventing
Overheating.
H. Collector Angle, Plane, and Direction
1. Collector Direction
The collector should face the equator. In the northern hemisphere,
this is due south, and in the southern hemisphere, due north. Facing
the collector in the correct direction and angle is important to ensure
optimal heat output. A deviation of up to 15
o
from due south is
acceptable, and will have minimal effect on heat output.
NOTE:
In Figure 2, D orientation (landscape) is not recommended for
drain back systems.
Figure 2 - Suggested Solar Collector Mounting Designs
2. Collector Angle (Tilt)
It is common for collectors to be installed at an angle that corresponds
to the installation latitude. While adhering to this guideline, an angle of
la/- 10
o
is acceptable, and will not greatly reduce solar output.
The solar collector should be installed at an angle between 20 – 80
o
to
ensure optimal operation.
For year-round domestic hot water, the collector should be tilted to
an angle of equal to the latitude of the installation site. Add 15
o
to the
latitude to optimize for winter performance (space heating). Subtract
15
o
from the latitude to optimize for summer performance (indirect
pool heating).
Given the formula above, a solar collector installed at 30
o
N latitude
should face due south at an angle of 45
o
for wintertime advantage,
and 15
o
for summertime heating.
Preventing Overheating
To reduce summer heat output, angle the collector for optimal
winter absorption. This is achieved by installing the collector at
an angle of around 15
o
above the latitude angle (e.g. 45
o
at 30
o
N
latitude). This angle corresponds closely to the angle of the sun in
the sky during the winter months, thus maximizing winter output.
Conversely, during the summer when the sun is high in the sky,
the relative collector surface area exposed to sunlight is reduced,
cutting overall heat production considerably (by about 15%). This
option is ideal for installations where solar thermal is being used for
space heating.
3. Collector Plane (Horizontal or Vertical)
The collector could be installed vertically, but may be installed at an
angle, such as sideways on a pitched roof. It is not recommended
to install a drain back system in the horizontal or landscape style. In
vertical installations, collectors should be installed with a 1/4” pitch
towards the supply port to facilitate the drain back process. See
more detail in Part 2, Section D, Number 3.
I. Avoid Shade
Collectors should be located so that shading does not occur between
9 AM and 3 PM local time. Partial shading due to small objects such
as antennas and flues is not of great concern.
J. Location
To avoid long pipe runs, the collector should be positioned as
close as possible to the storage tank. Storage tank location should
therefore be considered part of the location requirements of the
solar collector. The storage tank should be located as close as
possible to the most frequent draw off points in the building.
K. Expansion Tank
Expansion of HTF occurs as it heats. When HTF expands, it has to
be controlled, as fluid cannot be compressed like air. A properly
sized and installed expansion tank can accommodate expansion
of HTF. If the expansion tank fails, a properly sized and installed
PTRV will activate and protect the system. Failure to properly
control HTF expansion may result in property damage, personal
injury, or death.
See the following requirements for expansion requirements specific
to application.
NOTE:
Only authorized licensed contractors are permitted to install
the solar collector.
