Sundra 5-16 solar hot water system

A self-contained heating circuit transports the heat from the collector to the in-house hot-water storage tank (approx.300L). There the heat is passed on to the in-house hot-water storage tank by a heat exchanger and the water for domestic use is heated. When the heat supplied by the collector is not sufficient to attain the desired temperature, a conventional heating system takes over and completes the heating process. An electronic control unit (different-temperature regulator) constantly checks whether the temperature at the collector opening is greater than the temperature in the inhouse hot-water storage tank. If this is the case, the control unit switches on the heating circuit.

Source: Sundra SEIDO5 series Heat Pipe Vacuum Tube Solar Collector

Open Hot Water/Radiant System

Source: Radiant floor heating company: Solar water heating, The open system
The Open System

The Open Hot Water/Radiant System uses a heat exchanger to transfer thermal energy to a storage tank filled with potable water. This approach provides domestic hot water, radiant floor heat, and allows the system to be powered by a very low wattage pump.

A radiant heating system is considered "open" any time the same hot water is used for both radiant heating and domestic hot water. This type of system is very efficient because a single heat source (in this case, a hot water storage tank) provides for all the home's hot water needs. The homeowner doesn't need two completely separate systems, many times with overlapping mechanical components, performing separate heating tasks.

Note that cold water from the domestic supply enters the water heater via the floor tubing so that there's never any chance of stagnant water entering the domestic system. Fresh water enters the tubing every time hot water is used.

And although it looks at first glance as if cold water will be cooling down your floor, in reality that won't happen. The only cold water that can enter the tubing will be the "make up" water to your water heater. If no hot water valves are open in your domestic system, the radiant system is essentially "closed". In other words, cold water cannot enter the system unless there is an open hot water valve in the house somewhere. Normally, only the circulator pump supplying the radiant tubing can force water from the water heater into the tubing, and back, when your zone calls for heat.

Open system with solar tie-in

Solar water heaters interface well with radiantly heated floors because the large thermal mass common to radiant systems provides an excellent storage medium for the energy generated during the day. At night, this stored thermal energy is slowly released into the living space. The schematic below demonstrates how a solar thermal array can interface with an open radiant system.

The Stiebel-Eltron hot water tank has two heat exchangers into their storage tank. The lower (solar) coil heats the tank to a usable temperature, and the hot water is drawn off as needed for domestic and heating purposes. Fresh water enters the tank in direct proportion to the amount drawn off for domestic hot water. When hot water is taken from the tank for radiant heating purposes, it simply returns to the tank for re-heating.

Since solar panels can heat the tank to near boiling in the summer, a mixing valve tempers the potentially scalding water to a safe level. If cloud or winter limit the amount of sunlight , an on-demand (back-up) unit heats the upper coil so that hot water is always available for domestic or radiant heating purposes.

Solar heat dump

The solar heat dump prevents the water heater and solar collectors from overheating in the summertime. It moves heat away from the solar loop and into a copper coil. This coil will be buried under the middle of the house. A sensor at the entry of the water dump controls the flow.

Stiebel-Eltron Tank

The 300 L (80 gallon) Stiebel SBB - 300 solar storage tank is the central component of the solar hot water system, storing potable hot water for the hydronic floor and for domestic household use.

It collects solar heat by running fluid (antifreeze) from the solar collector through a heat exchanging coil at the bottom of the tank (see diagram below).

A back-up heat source (in our case, and electric boiler) provides heat through another heat exchanger coil in to top of the tank when the water gets below a set temperature. Electricity runs at 8 cents a KWh in Quebec, and it makes little sense to use anything else.
Sources:

• Radiant floor heating company: Solar Water Heating - Storage
• Stiebel-Eltron USA: SB and SBB Solar Storage Tanks
• Stiebel Eltron USA: Instalation guide

Technical Details


Dimensions

Evacuated tube collectors

Source: Radiant floor company

Use of solar energy to heat domestic hot water and radiant floors is soaring along with the cost of fossil fuels. New, more efficient heating technology, i.e. evacuated tube absorbers, makes solar even more desirable. Below is a description of the most commonly used methods of heating water with solar energy and the advantages and disadvantages of each.

Most people are somewhat familiar with the standard flat plate type solar collector. This collector is basically a highly insulated box containing a grid of copper pipes bonded to a flat black copper absorber plate. Special glass enhances solar absorption.

Evacuated tube collectors use multiple vacuum filled glass tubes, each with a tiny amount of antifreeze hermetically sealed within a small central copper pipe. When heated by the sun, this antifreeze converts to steam, rises to the top of the tube, transfers its heat to a collector header, then condenses back into liquid and repeats the process.

Because heat doesn't easily transfer through a vacuum, 92% of the thermal energy hitting the absorber plate stays within the evacuated tube and passes to the collector header. This is a huge advantage because a standard flat plate collector radiates much of its accumulated heat to the surrounding atmosphere like any other hot object.

The evacuated tubes are also completely modular. Although rarely necessary, one or more tubes can be removed and replaced without affecting the other tubes in the array. There is no actual liquid transferred from the evacuated tube to the collector header...just heat. Evacuated tubes also start absorbing heat earlier in the day than flat plates due to their convex design and the tiny amount of antifreeze within the tube is freeze protected down to -50 degrees below zero.

Source: Radiant floor company

Solar differential controller

Solar thermal systems generally use a special relay called a Differential Controller. This relay activates a pump when the temperature in the solar collector is hotter than the temperature at the bottom of the solar storage tank.

Two sensors (storage tank and solar array) are required for a proper "differential". One sensor is attached to a pipe near the bottom of the solar storage tank. The second sensor reads the water temperature as it leaves the solar collectors. Both sensors must be insulated (with fiberglass or foam) to prevent ambient temperature from influencing the reading. It should be noted that a sensor clamped to a hot pipe will NOT accurately read the actual water temperature. In fact, the water will generally be 15 to 20 degrees warmer than the sensor indicates.

Fortunately, for the purposes of a well functioning solar hot water system, actual water temperature is not important (unless, of course, it's too tepid for a hot shower). What matters is the difference between the water temperatures at the two locations. After all, if the water is actually hotter than what the sensor indicates, so much the better.

The DeltaSol® BS controller is available in 4 versions, depending on the demands.

Technical data
Size: 172 x 110 x 46 mm
Housing: plastic, PC-ABS and PMMA
Protection type: IP 20 / DIN 40050
Ambient temp.: 0 ... 40 °C
Mounting: wall mounting, mounting into patch-panels is possible
Operation: by 3 push-buttons at the
front of the housing
Functions: Differential temperature
controller with optional add-on system
functions. Function control, operating
hours counter for solar pump, tube
collector function, pump speed control,
thermostat function and heat quantity
measurement.
Inputs: for 4 temperature sensors Pt1000
Outputs: 2 semiconductor relays

Sources: Radiant floor heating company, Reso-Elektronische Regelungen GmbH

Sundra 5-16 solar collector - Manifold Header

Sundra 5- 16 Collector
Manifold headers have capacities of 8, 16 or 20 tubes (in our case, 16 tubes). The headers allow for a modular design as the heat transfer liquid flowing through the manifold to the solar tank does not flow through the collector tubes. The operation of the system will therefore not be interrupted even if one of the collector tubes is damaged.


Manifold Header
The manifold header pipe is mounted within the manifold casing and is made of F28 mm, 1 mm thick copper pipe. The condenser section of heat pipe is tightly inserted in the heat pipe port ensuring a dry connection between heat pipe and heat transfer fluid.

The collector manifold casing and the end cap are made of silver aluminium profile or brown aluminum plate and insulated with 50 mm thick, FC free polyurethane. The copper inlet and outlet pipe nipples come standard in OD 22 mm, making plumbing connections quick and easy using readily available metric compression fittings.

Technical specifications

Number of collector tubes	16
Absorber area	3.66 m²
Gross area	4.08 m²
Length x width x height (mm)	2126x960 x175mm
Weight	100 kg
Header box material	Aluminium alloy
Header box diameter	130 mm
Insulation	30mm polyurethane foam
Stagnation temperature, module	190°
Connection	Compression fitting, 22mm

Source: Sundra SEIDO5 series Heat Pipe Vacuum Tube Solar Collector

Contender solar tank - Specifications

Source: Heat transfer products - SolarStor Contender

This solar tank has a built in electric coil as backup, making a boiler unnecessary. It also features water input on top of the tank, making installation easy. Given the electric backup, it seems to make sense to use it.

Sundra 5-16 solar collector - Seido 5 Evacuated Tube

The Seido5 solar collecting tube contains a convex absorber plate encases in a 100 mm x 2000 mm vacuum tube. Originally developed for thermal control in satellites, the heat pipe vacuum tube absorbs up to 92% of the incoming irradiation.

Sunlight heats the dark blue absorber plates that transfer their heat to a heat pipe in the middle of the glass tube. The heat pipe consists of two meters of copper tubing with an evaporator section, a capillary wick structure, a condenser section and a small amount of vaporizable water. The evaporator section is tightly bonded to the absorber plate, where it captures the heat from the absorber and evaporates the water. The evaporated water moves up to the condenser section. The condenser protrudes out from the evacuated tube and is inserted into the heat exchanger manifold. Here, the water vapor is cooled and condensed into liquid form, transferring its heat to the fluid flowing through the manifold (anti-freeze, in our case). The liquid water is then pulled down the tube by gravity and this cycle begins again.

The lifespan of the tube is determined by how well the vacuum remains sealed. With wear, the seal breaks down and the system becomes less and less efficient over time. However, an inefficient tube will still produce hot waterallowing you to keep it past its estimated 10 year life. Moreover, modular nature of the tubes allows you to replace the tubes one at a time and with relative ease.

Technical Specifications

Type	SEIDO5
Specification	Heat pipe vacuum tube with bent absorber
Configuration
Absorber area	0.225 m²
Weight	4.7 kg
Installation tilt angel	35° – 90°
Dimension	Ø100mm x 2000mm
Collect heat pipe	Heat pipe copper Ø 8 mm
Absorber material	Copper- Aluminium sunstrip, 0.47 mm thickness
Selective coating	Aluminum nitride Al-N-O selective coating; Absorptance: a > 0.92; Emittance: e <>
Glass tube material	Borosilicate glass Thickness: 2.5 mm Transmittance of glass: 91%
Vacuum	<>
Min. ambient tem.	-45°C
Stagnation temp.	247°C
Resistance to hail	Ø35mm

Source: Sundra SEIDO5 series Heat Pipe Vacuum Tube Solar Collector

Expansion and purge kits (EPK)

Source: Radiant Floor heating company - Filling the closed system

Expansion and purge kits are necessary for the heated fluid entering the hot water tank from the solar collectors and the boiler. Closed loops circulate the same fluid around and around, completely separate from the domestic water supply in the Stiebel Eltron tank. The expansion tank allows the fluid to expand with heat. Fluid is added when the system is installed through valves, and can be purged and replaced as needed. Each kit consists of an expansion tank, valves, and pressure gauges that allow fluid to enter and leave the circulation piping.

Normally, hot water from the boiler or antifreeze from the solar collectors enter from the left, travel through the Expansion and Purge Kit (EPK) and into the hot water tank.