- Why is this a better collector than a flat plate?
There are various reasons:
1. Higher yearly efficiency due to the superior insulation provided by
the vacuum. This makes vacuum tube collectors much better for winter space
heating applications as well as all year DHW.
2. Easier Installation & Servicing – tubes are installed/removed
individually without special tools. You don’t have to shut the system down
if a tube is removed due to the dry connection to the heat exchange manifold
(no leakage potential)
3. Longer Life – absorber surfaces are protected from environmental
degradation by the hermetically sealed glass tube.
4. Tubes Rotate – at installation the tubes can be adjusted on axis to
compensate for non-south-facing roofs (flat plates require building a frame
to tilt the array)
- How do Sunda collectors compare to and so called
“double glass wall” products?
In Sunda evacuated tubes the absorber surface
and heat pipe reside in the vacuum environment, which prevents any
deterioration in long-term performance. This is not the case with the double
glass wall tubes in which both absorber and heat pipe are open to ambient
air. Being exposed to air, the copper to aluminum interface between absorber
plate and heat pipe is subject to oxidation which may lead to degraded
performance over time. Double glass wall tubes are also subject to
collection of water from condensation which could freeze and break glass
tubes in frost prone environments. These concerns are not applicable to the Sunda design.
- Will the glass break in a hailstorm?
The tubes are manufactured and tested to
withstand 35mm (1.38 inch) diameter hailstones. The glass is low-iron
tempered glass that is 2.5mm thick.
- How can you tell if you have lost the vacuum?
All tubes now being delivered have a silvery
coating on the inside at the bottom of the tube. When vacuum is lost, this
coating depletes and the tube becomes clear. Older style tubes did not have
this feature and you had to rely on observing a build-up of condensation
inside the tube as an indicator of vacuum loss.
- How many tubes do you need and how much space is
required?
For DHW we typically use 4 tubes per person,
which assumes 20 gal/person/day usage rate and raising the water temperature
from say 55 F to 120 F at a minimum. A 2-person family would need a Seido
1/5-8 tube collector and a 50 gal storage tank. A 4-person family needs a
Seido 1/5-16 tube collector and an 80 gal tank. The 16-tube collector is
just over 6ft wide (75.6”) and about 7 ft long (83”).
- Can I heat my house with these?
Yes, provided that the home is well insulated,
thereby having a low heat loss to the environment. There are no rules of
thumb for sizing a space heating array based on square footage of a house.
You have to know the heat loss, design temperatures, weather data, and solar
radiation available to estimate the size. It will be larger than the DHW
component alone.
- Is there a potential of overheating?
Yes, any solar thermal collector can overheat
if the circulator is off during peak sun hours for a long period of time.
The pressure relief valve guards against damage to the system components.
The tubes will not “blow-up” or break due to high temperatures.
- What is the warranty?
Six full years unconditional on the tubes. If
you lose a vacuum seal during the first six years after purchase, you
receive a replacement tube free (shipping costs extra).
- How heavy is the collector?
Only 110 lbs for the 8-tube, and 220 for the
16-tube when fully assembled.
- How much do they cost?
Depending on the model, if you include the
tubes and the rest of the collector (frame, header, nuts & bolts) the retail
cost comes to about $100 on a per tube basis.
- What is the payback or ROI?
Easily half as long as PV but and on the order
of 5-7 years when compared to heating water with electricity. It depends on
usage and cost of energy. Ask yourself, “what is the payback on a
conventional water heater from the local home center?” Answer, “none” – you
just pay and pay and pay from the moment you install it. What is your energy
independence worth to you? It should be “priceless”.
- How are they shipped?
Collectors are crated and shipped by common
carrier. Only single replacement tubes can be shipped via UPS.
- What is the life of a tube?
The statistical “mean life to failure” is 15
years.
- Are these new?
No, the technology is about 20 years old. The
Sunda tubes were developed in Germany by Daimler-Benz Aerospace in
cooperation with Sunpu, a Chinese solar energy research company.
- Why does one tube have a straight absorber and the
other a bent one?
Seido 1 tubes have a straight absorber. These
tubes can be rotated on axis to compensate or non-south-facing roofs. The
Seido 5 tubes have a convex absorber providing 20% more surface area. They
produce more heat per day than the Seido 1’s but cannot be turned on axis
and should therefore be used only for true south-facing roofs (+/- 10 deg).
- Which side of the absorber in the tubes should face
to the sun?
Regardless of which Seido tube is used, always
face the blue side to the sun. It is treated with a selective coating which
absorbs the most energy from the sun’s rays as possible.
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