Solar Water Heating Bob Ramlow Chapter 5: Solar Water Heating Systems Bruce Hesher Engineering Technology Brevard Community College

Introduction p65 : Basic Terms Direct Systems (Open Loop): The (potable) water that will be used goes through the collector. Indirect Systems (Closed Loop): A heat transfer fluid is heated in the collector and a liquid to liquid heat exchanger transfers the heat into the water that will be used. Collector may be flat plate or evacuated tube. Passive Systems: Water is circulated without the use of pumps. Few if any moving parts and no external energy need to operate! Reliable but requires tank to be above collector. Active Systems: Use pumps and some form of energy to circulate fluids.

Open-loop Systems: All open-loop systems are direct and active. They use pumps and circulate the potable water through the collector. The collector is plumbed in parallel with the tank. Closed-Loop Systems: The heat transfer (solar fluid) remains in a separate circuit at all times. All closed loop systems are indirect. Can be flat plate, evacuated tube, or concentrating collectors. Two-Tank Systems: Use storage tank for heated water and some type of backup heater. These are called ‘two tank’ systems. Systems with a storage tanks and heater element or gas tank are one tank. The problem with one tank systems is they can use purchased energy to heat if the sun is not up when the hot water is used. So, Install a timer!

Introduction Basic Principles Hot Water Rises: When heat is added the molecules expand; this causes the volume to increase but not the mass, so it is lighter. The process of hot water rises is called stratification. Water Expands when it Freezes: Water shrinks as it is cooled but, when it changes state from liquid to solid it expands! Ice cubes float! The force generated by freezing is strong. If the collector freezes it will probably break some pipes. Water Quality: Most locations have “hard water”, water containing minerals. Water softeners remove minerals from water. When water is heated, dissolved minerals can precipitate out of solution a deposit on surfaces. See p 68.

Freezing in winter is the bane of SWH systems. There are 3 types of domestic hot water systems that are recommended: Freezing in winter is the bane of SWH systems. There are 3 types of domestic hot water systems that are recommended: ICS: have large volume so don’t freeze over night. Still ICS: have large volume so don’t freeze over night. Still not recommended for areas with long cold periods. not recommended for areas with long cold periods. Drainback: have air in collector loop for expansion Drainback: have air in collector loop for expansion Closed loop: have propylene glycol (antifreeze) in Closed loop: have propylene glycol (antifreeze) in collector loop. collector loop. Recommendations In Florida In Florida direct/open-loop, active, one-tank systems are popular. Most use Dole (freeze) valves. The Dole/freeze valves are a weak point. I recommend draining the collector on cold nights. PV panels to power the pump are popular. Be sure to put a timer on the electric backup. In Florida direct/open-loop, active, one-tank systems are popular. Most use Dole (freeze) valves. The Dole/freeze valves are a weak point. I recommend draining the collector on cold nights. PV panels to power the pump are popular. Be sure to put a timer on the electric backup.

Pressurized Antifreeze Systems p69 Most versatile of all system types and most widely distributed worldwide. Mounting of the flat plate collector can be in any orientation. Used everywhere except hot climates. Only fail-safe system for climates that experience freezing conditions. Can use flat plate or evacuated tube collectors. Most versatile of all system types and most widely distributed worldwide. Mounting of the flat plate collector can be in any orientation. Used everywhere except hot climates. Only fail-safe system for climates that experience freezing conditions. Can use flat plate or evacuated tube collectors.

Pressurized Anti-freeze System Rules p70 Line between exchanger and collector also needs to be copper or stainless but 180°F copper can be used. In large solar space heating systems the piping can be PEX except the last 10 feet from the collector. Collectors arrays should be mounted with a slight slope toward the inlet tube to permit draining. All horizontal pipe runs should be supported every 5-6ft. Loose pipes can sag may crack and may cause weird noises! The supply pipe between collector and heat exchanger must be copper or stainless steel and insulated with 250°F insulation.

Drainback Systems p77 This popular type of system works well in warm climates that do not experiences long periods of freezing temperatures. They use a storage tank and a drainback tank. When the system gets to its maximum temp the fluids drain out of the system to prevent overheating and damaging them. This popular type of system works well in warm climates that do not experiences long periods of freezing temperatures. They use a storage tank and a drainback tank. When the system gets to its maximum temp the fluids drain out of the system to prevent overheating and damaging them.

Integral Collector Storage Systems (ICS) See diagram p82 These passive direct systems have no pumps and the useable water goes through the collector. Some are two tank systems with storage both in collector and tank. The ICS is plumbed in series between the water supply and the tank. If the out of the collector is warmer than the setting on the tank the element will not activate. These passive direct systems have no pumps and the useable water goes through the collector. Some are two tank systems with storage both in collector and tank. The ICS is plumbed in series between the water supply and the tank. If the out of the collector is warmer than the setting on the tank the element will not activate. If the collector is colder than the incoming water the system cools the water causing you to buy more energy! ICS systems are low cost. The collector is heavy when full of water. Only use where there is no chance of freezing!

Thermo Siphon Systems p84 Use the fact that hot water rises/cold water falls. Storage tank must be above collector! They are passive, low cost, and reliable. Use the fact that hot water rises/cold water falls. Storage tank must be above collector! They are passive, low cost, and reliable. Thermo siphon systems can be direct or indirect. Direct systems usually use a flat plate collector. See diagram p66.

Open-Loop Systems (common in Florida) These systems have water in the collector at all times. Composed of a storage tank and collector, circulating pump and controller (or PV panel). The collector is plumbed in parallel with the storage tank. When the controller sees the collector is sufficiently warmer than the tank, it turns on the pump. These systems have water in the collector at all times. Composed of a storage tank and collector, circulating pump and controller (or PV panel). The collector is plumbed in parallel with the storage tank. When the controller sees the collector is sufficiently warmer than the tank, it turns on the pump. These systems must have freeze protection even in Florida! These systems must have freeze protection even in Florida!

Draindown Systems p87 All draindown systems are direct. They use a special drain down valve controlled by a differential controller to send water through the collector. When the sun sets or is blocked by clouds the pump shuts off and the water that was in the collector is allowed to drain down out of the collector and piping. This small amount of water is piped to a floor drain and is lost. All draindown systems are direct. They use a special drain down valve controlled by a differential controller to send water through the collector. When the sun sets or is blocked by clouds the pump shuts off and the water that was in the collector is allowed to drain down out of the collector and piping. This small amount of water is piped to a floor drain and is lost.

Refrigerant Solar Water Heaters (Heat Pump water Heaters) Heat Pump water heaters use electricity to move heat from one place to another instead of using it to do the heating. Work on the principle that fluids absorbs energy when it vaporizes and when it condenses, heat is released into the storage tank. Use Freon. Can work at very low temperatures when liquid collectors do not. Can work on cloudy days or in a room at indoor temps. Tend to cool the room they are in. Heat Pump water heaters use electricity to move heat from one place to another instead of using it to do the heating. Work on the principle that fluids absorbs energy when it vaporizes and when it condenses, heat is released into the storage tank. Use Freon. Can work at very low temperatures when liquid collectors do not. Can work on cloudy days or in a room at indoor temps. Tend to cool the room they are in. See p89 for pros & cons. See p89 for pros & cons.

Solar Heated Pools There are 18 times as many solar pool heating systems installed each year in the U.S. than any other type of solar heater because they are so cost-effective. Payback is 1-2 years compared to electric or gas. There are 18 times as many solar pool heating systems installed each year in the U.S. than any other type of solar heater because they are so cost-effective. Payback is 1-2 years compared to electric or gas. There are 2 ways to increase the temperature. 1) Add more heat. 2) Reduce heat losses. See

Add More Heat A temperature controlled flow valve diverts water through the solar thermal panel iff the pool water is not warm enough. Florida law forbids all but licensed roofing contractors or CGC solar contractors from installing solar on your roof.

Reduce Heat Losses The most effective way to reduce heat losses is to cover the surface of the pool. Pool blankets are inexpensive and do not have any of the risks associated with installing equipment on the roof.

Solar Heated Spas & Hot Tubs A hot tube or spa should be well insulated! The surface are is much smaller than that of a swimming pool and therefore easier to insulate. Because pools & spas have chemically treated water, all piping should be made of PVC. If there is both a pool and a spa, you can use a poll heating system and return the water to the pool by putting it into the spa. The overflow from the spa would go into the pool. The small volume well insulated spa would get much warmer than the pool and not lose enough of the heat to cool the pool significantly.