Steamback Shows Promise for Solar Water Overheating
Commercial and residential customers install solutions that heat their water, businesses and homes. But what happens when there is too much of a good thing? Solar water heating systems can and do overheat, creating both inconvenience and cost for the customer. But a European technique called steamback or vapor drainback provides multiple advantages over existing technologies, including fewer service calls, more system uptime, and reduced overall costs.The two primary causes of overheating in solar systems are underuse of the heated water and electrical power outages. The former is rare in winter months, but can wreak havoc during the summer months, especially since those periods often correspond with family vacations and there may be no hot water demand for days or weeks at a time. The latter is all too common, particularly during thunderstorm season when a freak storm knocks out power and is followed by a bright sunny day. It only takes an outage of an hour or two of sun without circulation to cause the system to overheat.
There are multiple design options to ensure systems don’t overheat, but as our industry grows and matures, installers know that customers demand a robust solution. Few customers want to invest significant sums to mitigate a relatively infrequent situation. Historically most closed-loop solar hot water systems have relied on control strategies that either dump excess hot water from the tank into a drain, or on dump zones which dump heat from the solar loop itself once the tank has reached a certain set point. Those strategies work, but the first wastes water and the latter wastes electricity, and both introduce additional costs and failure points to the system.
More recently, solar pump controllers with advanced logic allow the installer to set up night time recirculation to scrub excess heat from the solar tank at night when the collectors are cooler. But nighttime recirculation also increases parasitic power and furthermore doesn’t work all that well for systems designed with well-insulated collectors (for example evacuated tube collectors).
As a last resort, most systems rely on pressure-relief valves (PRVs) that when activated, protect against dangerous and damaging overpressure in the system, but also make a mess and completely shut the system down. Restarting the solar hot-water system then requires a service call and a technician with a fill pump to recharge and repressurize the system.
Indiana Energy Insights: OED's Bloomingfoods Visit
The next time you're in Bloomington, make sure to swing by Bloomingfoods to take a look around. Bloomingfoods is a repeat grant recipient of OED's. Last year, they installed a 4.4 kW photovoltaic solar array, and this year, they used a Solar Thermal Grant from OED to install a solar thermal drain-back system for heating the store's domestic water supply. (These are at separate locations, by the way.) Due to its freezing and overheating prevention, the drain-back system was a great choice for replacing Bloomingfoods's older, 100-gallon commercial water heater. Hot water is needed for in-store cleaning, food production, and other services throughout the store. Whether or not they know it, this system is a great help and asset for the 8,300 member owners and the 1,000+ people who walk in the door!
Solar Drainback Systems - Bookshelf
Planning and Installing Solar Thermal Systems, A Guide for Installers, Architects and Engineers
3.3.5 Drain back system Figure 3.9. WW CW AH CW WW AH With this system the domestic water heating is carried out, just as with a standard solar system, ...Solar Domestic Water Heating, The Earthscan Expert Handbook for Planning, Design and Installation
7.4 Active drainback indirect systems Categories: active; indirect, drainback, solar storage external and internal Typical climate: all The main advantage ...Solar Power Your Home For Dummies
Note the bypass valves, which allow water to bypass the solar collector and revert to ... Installing a Drainback System for Most Climates Indirect, active, ...Solar heating systems for houses, a design handbook for solar combisystems
Manufacturers such as Atag Verwarming and ZEN Solar have developed this idea over a number of years into foolproof drainback systems (Noij, 2001). ...Heating Services in Buildings
DRAIN-BACK SOLAR HEATING SYSTEMS The drain-back or drain-down solar heating system is an alternative arrangement for systems that may be subjected to ...Information Source Directory
Drainback solar heaters for cold climates
There are two main types of solar heating systems for cold climates: drainback solar heating systems and Antifreezing solar closed-loop systems. ...
Drainback Solar Water Heater Systems (Traditional)
Specially designed Drainback Solar Water Heater Systems can convert any regular water heater to a solar water heater!
Simple Drainback System (Active)
This solar system uses SRCC OG-100 Certified 4x8 or 4x6.5 EZINC Thermal Collectors! ... The Simple Drainback Tank serves as a low pressure solar fluid reservoir for the system. ...
Solar Water Heating Projects and Plans
Descriptions and plans for several types of solar water heating systems, including batch systems, drainback systems, and closed loop systems.
Solar Thermal Drainback Systems
Solar thermal drainback systems eliminate a lot of problems found in other systems. Find out if this system is right for you here.