Solar Water HeatingSolar Water HeatingBob RamlowBob Ramlow

Chapter 6: Chapter 6:

Solar Space Heating SystemsSolar Space Heating Systems

Bruce HesherBruce Hesher

Engineering TechnologyEngineering Technology

Brevard Community CollegeBrevard Community College

Solar Space HeatingSolar Space Heating ( (SSHSSH) is using the sun to heat the living ) is using the sun to heat the living space of a home or building. A significant portion of fossil fuel space of a home or building. A significant portion of fossil fuel consumed and household budgets goes to heating homes & consumed and household budgets goes to heating homes & buildings.buildings.

An An activeactive solar space heating system uses a collector to solar space heating system uses a collector to capture and use the sun’s energy. A capture and use the sun’s energy. A passivepassive system uses the system uses the building itself as a solar collector. The text covers active building itself as a solar collector. The text covers active systems.systems.

DefinitionsDefinitions

Conservation & WeatherizationConservation & Weatherization

Most existing and many new buildings are not made with energy Most existing and many new buildings are not made with energy conservation in mind. The best return on investment for heating is conservation in mind. The best return on investment for heating is energy conservation. energy conservation.

If you have done a good job of venting the attic to keep it cool in the If you have done a good job of venting the attic to keep it cool in the summer, you have also made it loose heat in the winter. The way to summer, you have also made it loose heat in the winter. The way to have your cake and eat it too, is to insulate the attic floor very well.have your cake and eat it too, is to insulate the attic floor very well.

On cold winter days (yes we do have them On cold winter days (yes we do have them in Florida) you can also cover any solar in Florida) you can also cover any solar attic vents. This is not practical with ridge attic vents. This is not practical with ridge vents.vents. Deciduous trees that shade in summer Deciduous trees that shade in summer but drop their leaves in winter are good.but drop their leaves in winter are good.

Attic and Exterior Wall Insulation

Most homes in Florida do not have enough Most homes in Florida do not have enough insulation. Inspect your attic. Fiberglass batting insulation. Inspect your attic. Fiberglass batting that is the depth of a 2x4 truss has about R-15. that is the depth of a 2x4 truss has about R-15. For R-30, run a second layer using care not to For R-30, run a second layer using care not to block soffit vent air flow. block soffit vent air flow.

The DOE recommends that homes in zone The DOE recommends that homes in zone 2 (Florida) have R-30 to R-60. Insulation 2 (Florida) have R-30 to R-60. Insulation improves both heating and cooling costs!improves both heating and cooling costs!

Puncture the vapor barrier with a small pointed object like a nail, placing holes 2-3 inches apart to prevent moisture build up between layers.

Low Winter Solar ResourceLow Winter Solar Resource

A solar space heating system will not meet 100% of a A solar space heating system will not meet 100% of a buildings heating requirements, buildings heating requirements, nor is it a cost effective nor is it a cost effective goal to try to achieve.goal to try to achieve. Clouds and short winter days take Clouds and short winter days take their toll. Sizing a system to meet the heating needs on the their toll. Sizing a system to meet the heating needs on the coldest time of year will result in a system that wastes a lot coldest time of year will result in a system that wastes a lot of heat during the rest of the year. of heat during the rest of the year.

A better strategy is to size the systems to provide the heat A better strategy is to size the systems to provide the heat needed on a sunny winter day.needed on a sunny winter day.

Some active solar space heating systems have energy Some active solar space heating systems have energy storage while others do not. storage while others do not.

System TypesSystem Types

After solar pool heating and solar water heating systems, After solar pool heating and solar water heating systems, solar space heating systems are the most cost effective. solar space heating systems are the most cost effective.

The 2 most popular types of space heating systems are:The 2 most popular types of space heating systems are:

air-type air-type –– Using air passages and dampers.Using air passages and dampers.

and and

liquid-type liquid-type - Became popular in 1980’s and are still today. - Became popular in 1980’s and are still today. Some have storage. If you have a SWH systems, the most Some have storage. If you have a SWH systems, the most effective strategy is to use a combination SWH and SPH effective strategy is to use a combination SWH and SPH system.system.

Liquid-Type Solar Heating Systems Liquid-Type Solar Heating Systems p99p99

Became popular in the 1980’s. Some have storage, Became popular in the 1980’s. Some have storage, others don’t. others don’t. SSolar olar WWater ater HHeating systems are the most eating systems are the most cost effective; cost effective; SSolar olar SSpace pace HHeating systems are next. eating systems are next. Solar Water Heating saves money year round, solar space Solar Water Heating saves money year round, solar space heating saves money in winter. heating saves money in winter.

If you want to use solar energy to heat your building and If you want to use solar energy to heat your building and you have SWH system a combination system is a good you have SWH system a combination system is a good option. In a combination SWH and SSH system the option. In a combination SWH and SSH system the collectors should be tilted toward the winter sun to collectors should be tilted toward the winter sun to maximize production in the cold month’s. maximize production in the cold month’s.

Liquid-Type Systems without Liquid-Type Systems without Storage Storage p99p99

Systems without storage are also called dump systems. They simply dump any heat produced into the building. They use a liquid to air heat exchanger with liquid only in the collector loop.

A drainback SSH systems works much like a SWH drain back system. They use a heat exchanger with a pump that simply shuts off if the building temperature reaches the desired temp.

There are also closed loop anti-freeze SSH systems without storage.

Drainback Solar Heating Systems Without StorageDrainback Solar Heating Systems Without Storage p100p100

• Same solar loop as drainback SWH system. Combination Same solar loop as drainback SWH system. Combination SWH & SSH possible with over sized collector(s).SWH & SSH possible with over sized collector(s).

• Once building up to temp the system simply shuts off.Once building up to temp the system simply shuts off.• No issue with over heating collector loop fluid in hot No issue with over heating collector loop fluid in hot

season.season.• Reliable - less components than pressurized systemsReliable - less components than pressurized systems• Energy efficient - Only run when controller sees heat to Energy efficient - Only run when controller sees heat to

garner. garner. • Freeze tolerant - No water in collector when cold.Freeze tolerant - No water in collector when cold.• Drainback tank must be above storage tank.Drainback tank must be above storage tank.

Pressurized Solar Heating Systems without StoragePressurized Solar Heating Systems without Storage p101p101

Solar fluid is sent directly to heat delivery system. The Solar fluid is sent directly to heat delivery system. The mass of the building and contents serves as storage. mass of the building and contents serves as storage.

These systems are always on. Care must be used to These systems are always on. Care must be used to prevent anti-freeze fluid in collector from overheating. Let prevent anti-freeze fluid in collector from overheating. Let system run even on a hot day. (won’t fly in Florida). Can system run even on a hot day. (won’t fly in Florida). Can use diversionary load consisting of pipes buried in the use diversionary load consisting of pipes buried in the ground outside of the buildings footprint. ground outside of the buildings footprint.

Liquid-Type Systems with Storage Liquid-Type Systems with Storage p101p101

Can be thought of as expanded SWH systems. Again there Can be thought of as expanded SWH systems. Again there are several types to choose from depending on climate and are several types to choose from depending on climate and other factors.other factors.

Drainback systems:Drainback systems:

Single tank systems.Single tank systems.

One drainback tank and one or more heat storage tanks.One drainback tank and one or more heat storage tanks.

Closed-loop systems:Closed-loop systems:

Single tank systems.Single tank systems.

Several heat tanks.Several heat tanks.

Sand heat storage.Sand heat storage.

Solar “heat dump” SystemSolar “heat dump” System

A system without heat storage that puts all the heat it gathers into the building directly without any attempt at storage can be effective. These systems actually have some heat storage because the building itself and its contents hold heat.

A brick or cement block house will hold heat for a couple days.

A full freezer will stay cold longer without power than A full freezer will stay cold longer without power than an empty one.an empty one.

Heat Storage Configurations Heat Storage Configurations p102p102

Large single tanks:

Open (unpressurized) with tight fitting lid. Seamless and joint less is desirable. Made of material that can withstand continuous 180°F. Well insulated.

Must fit into the building! A 400 gal tank is 6ft tall and 4ft in diameter.

Since fittings are sources of leaks, tanks with all fittings on top is good.

Heat Delivery Methods Heat Delivery Methods p110p110

There are several option for getting stored heat into the building depending on existing heat delivery system and storage method.

Integrating a solar and a fossil fuel heating system:

Sometimes easy, Sometimes not. There are many of fossil fuel systems. Consult the heating contractor that installed the fossil fuel system.

Integrating a solar and a forced air system:

Commonly done in retrofits. Forced air systems use a lot of electricity for fans, not recommend for new buildings.

High-Mass Systems High-Mass Systems p119p119

Radiant flooring was first used by the Romans 2,000 years ago! Radiant flooring provides comfortable heat at low cost. Radiant flooring systems use closed loop anti-freeze collection systems and circulate the heated fluid under the building (or in the foundation) to store the heat in the sand below the building or the concrete slab.

As the heat rises it warms the As the heat rises it warms the building. Radiant flooring has a building. Radiant flooring has a very high thermal mass that takes very high thermal mass that takes a long time to heat and a long time a long time to heat and a long time to cool. The long cooling time can to cool. The long cooling time can keep a building warm for days.keep a building warm for days.

NoteNote: It is also possible to run cool water through the : It is also possible to run cool water through the radiant flooring iff you have a source of cool water!radiant flooring iff you have a source of cool water!

Air-Type Solar Heating Systems Air-Type Solar Heating Systems p124p124

These systems are cost effective because the equipment These systems are cost effective because the equipment is simple and low cost. Air (free) is the heat transfer is simple and low cost. Air (free) is the heat transfer mechanism. Ductwork (may already exist) is used to move mechanism. Ductwork (may already exist) is used to move heat into the building. Most popular in climates with large heat into the building. Most popular in climates with large heating loads. Used strictly for air and not for water heating loads. Used strictly for air and not for water heating. heating.

One downside is that they need a large blower fan to One downside is that they need a large blower fan to circulate the heat. Since circulation is need when the air in circulate the heat. Since circulation is need when the air in the collector is warm and this means the sun is up, PV can the collector is warm and this means the sun is up, PV can power the fan.power the fan.

Further Investigation

www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

www.doe.gov search for “solar space heating”

www.house-energy.com/Solar/System-Drainback.htm