CONIFER SOLAR CONSULTING

Jon Klima, Owner
360 Trout Lane, PO Box 23, Guffey, CO 80820
Phone: 719 479-2281,  Email: jon.klima@gmail.com
In business for 37 years

 

Generic Solar Domestic Hot Water Heating System Descriptions

 

All system diagrams shown below are typical generic solar domestic hot water heating systems. Many variations of each system are possible and will work equally well. The purpose of presenting these drawings is simply to give you an idea of some of the different solar heating systems available.

 

The Antifreeze SDHW System

 

The closed-loop-antifreeze DHW system consists of two loops; the heat collection loop and the heat delivery loop. Let's first look at the heat collection fluid loop. Starting at the pump (lower left portion of the diagram), fluid will be pumped through the flow gauge and up to the collector panels. Here, the panels will absorb energy from sun and transfer this energy, in the form of heat, to the collection fluid. The fluid will then return down to the the heat exchanger.

Antifreeze SDHW System

Here, heat will be transferred from the collection fluid side of the heat exchanger to the cooler potable water side. The collection fluid will then complete it's loop by flowing from the heat exchanger, through the check valve, and back to the pump. The job of the expansion tank is to allow for the expansion and contraction of the heat collection fluid as it heats up and cools down.

 

The pump in the potable water loop turns on at the same time as the heat collection loop pump and circulates water from the solar pre-heater tank through the heat exchanger, where it absorbs heat from the warmer heat collection fluid flowing through the heat collection side of the heat exchanger. The potable water then returns through the check valve to the solar pre-heater tank. The controller continually monitors the sensors located at the solar collector panel and the solar pre-heater tank. When the temperature at the collector sensor exceeds the temperature of the solar tank sensor by a pre-determined amount, usually 12 - 20º F, the controller turns the pumps on. The pumps stay on until the temperature difference between the panel and solar tank sensors drops to about 5º F.

 

When a person opens a hot water faucet, cold water enters the solar pre-heater tank through the normally open (N.O.) valve shown above the pre-heater. Warm water from the pre-heater then flows through the N.O. valve between the two tanks and enters the standard water heater. If the water in the standard tank drops below the thermostat set point, the gas (or electric) will turn on and heat the water to the thermostat set point. The hot water then flows from the tank, through the tempering valve, and on to the faucet. If the water is above the tempering valve's set point, the valve will allow cold water to enter and mix with the hot to avoid a user at the faucet from being scalded. The normally closed (N.C.) valve above the standard water heater is opened only when the solar system needs to be by-passed for service work. When this happens, the two N.O. valves would then be closed.

 

 

The Drain Back SDHW System

 

The drain-back DHW system consists of two loops; the heat collection loop and the heat delivery loop. This type of system uses water as the heat collection fluid. Let's first look at the heat collection loop. Starting at the pump (lower left portion of the diagram), water will be pumped through the flow gauge and up to the collector panels. Here, the panels will absorb energy from the sun and transfer this energy in the form of heat, to the water.

The water will then return down to the heat exchanger. Here, heat will be transferred from the collector side of the heat exchanger to the cooler potable water side.

 

The water will then complete it's loop by flowing from the heat exchanger, through the drain-back tank, and back to the pump. The job of the drain-back tank is to provide a space for the water to drain when the pump turns off and a space for the air to go when the pump turns on and forces the air from the collector panels. Allowing the water to return to the drain-back tank when power is removed from the pump is how freeze protection of the collector panels is accomplished. The pump in the potable water loop turns on at the same time as the heat collection loop pump and circulates water from the solar pre-heater tank through the heat exchanger, where it absorbs heat from the warmer heat collection side of the heat exchanger. The potable water then returns through the check valve to the solar pre-heater tank. The controller continually monitors the sensors located at the solar collector panel and the solar pre-heater tank. When the temperature at the collector sensor exceeds the temperature of the solar tank sensor by a pre-determined amount, usually 12 - 20º F, the controller turns the pumps on. The pumps stay on until the temperature difference between the panel and solar tank sensor drops to about 5º F.

 

When a person opens a hot water faucet, cold water enters the solar pre-heater tank through the normally open (N.O.) valve shown above the pre-heater. Warm water from the pre-heater then flows through the N.O. valve between the two tanks and enters the standard water heater. If the water in the standard tank drops below the thermostat set point, the gas (or electric) will turn on and heat the water to the thermostat set point. The hot water then flows from the tank, through the tempering valve, and on to the faucet. If the water is above the tempering valve's set point, the valve will allow cold water to enter and mix with the hot to avoid a user at the faucet from being scalded. The normally closed (N.C.) valve above the standard water heater is opened only when the solar system needs to be by-passed for service work. When this happens, the two N.O. valves would then be closed.

 

 

The Drain Down SDHW System

 

With a drain-down DHW system, the heat collection loop and the heat delivery loop are combined into one loop. Water, the same water that ultimately flows from the hot water faucet, is circulated through, and heated by the solar collector panels. Starting at the pump, water is pumped through a pair of ports in the drain-down valve and up to the collector panels.

Here, the panels absorb energy from the sun and transfers this energy, in the form of heat, to the water. The water then returns down, and flows through a different set of ports in the drain-down valve, then on to the solar storage tank.

 

The drain-down valve ports remain in the "fill" position as long as the controller applies power to the valve. This continues as long as the collector panel sensor remains above about 42º F. The controller continually monitors the sensors located at the solar collector panel and the solar pre-heater tank. When the collector panel sensor drops below 42º F, the controller removes power from the drain-down valve and it changes position to the "drain" position. This allows the water to drain out of the panels as air enters through the vacuum breaker atop the panels. When the collector panel sensor raises to about 52º F the controller re-applies power to the drain-down valve and it returns to its fill position. Additionally, when the temperature at the collector sensor exceeds the temperature of the solar tank sensor by a pre-selected amount, usually 12 - 20 º F, the controller turns the pump on. The pump stay on until the temperature difference between the panel and solar tank sensors drops to about 5º F.

 

 

The Two Tank Recirculation SDHW System

 

With a recirculation DHW system, the heat collection loop and the heat delivery loop are combined into one loop. Water, the same water that ultimately flows from the hot water faucet, is circulated through, and heated by the solar collector panels. Starting at the pump, water is pumped through a check valve and up to the collector panels.

Here, the panels absorb energy from the sun and transfers this energy, in the form of heat, to the water. The water then returns down, and flows directly into the solar pre-heater storage tank. The controller continually monitors the sensors located at the solar collector panel and the solar pre-heater tank.

 

When the temperature at the collector sensor exceeds the temperature of the solar tank sensor by a pre-determined amount, usually 12 - 20º F, the controller turns the pumps on. The pumps stay on until the temperature difference between the panel and solar tank sensors drops to about 5º F.

 

When a person opens a hot water faucet, cold water enters the solar pre-heater tank through the normally open (N.O.) valve shown above the pre-heater. Warm water from the pre-heater then flows through the N.O. valve between the two tanks and enters the standard water heater. If the water in the standard tank drops below the thermostat set point, the gas (or electric) will turn on and heat the water to the thermostat set point. The hot water then flows from the tank, through the tempering valve, and on to the faucet. If the water is above the tempering valve's set point, the valve will allow cold water to enter and mix with the hot to avoid a user at the faucet from being scalded. The normally closed (N.C.) valve above the standard water heater is opened only when the solar system needs to be by-passed for service work. When this happens, the two N.O. valves would then be closed. Water, the heat collection fluid used with this type of system, is never automatically drained from the heat collection loop. As a result, such a system should never be used where freezing temperatures are to be expected on a regular basis. These systems should be limited to the very southern parts of the U.S. Provisions for manual draining of the system are a must since even the very southern parts of the U.S. can experience a freeze now and then. Recirculation systems have controls that allow the heat circulation pump to turn on to circulate the water through the collectors during freezing conditions. This simply circulates warm water from the solar storage tank to the solar collectors, and this keeps the collectors from freezing. This works well as long as there is power to keep the pump running and enough warm water in the solar storage tank to last out the freeze spell.

 

 

The Single Tank Recirculation SDHW System

 

With a recirculation DHW system, the heat collection loop and the heat delivery loop are combined into one loop. Water, the same water that ultimately flows from the hot water faucet, is circulated through, and heated by the solar collector panels. Starting at the pump, water is pumped through a check valve and up to the collector panels.

Here, the panels absorb energy from the sun and transfers this energy, in the form of heat, to the water. The water then returns down, and flows directly into the water storage tank. The controller continually monitors the sensors located at the solar collector panel and the solar storage tank.

 

When the temperature at the collector sensor exceeds the temperature of the water tank sensor by a pre-determined amount, usually 12 - 20º F, the controller turns the pumps on. The pumps stay on until the temperature difference between the panel and water tank sensors drops to about 5º F.

 

When a person opens a hot water faucet, cold water enters the water tank through the normally open (N.O.) valve shown above the water heater. If the water in the water heater tank drops below the thermostat set point, the gas (or electric) will turn on and heat the water to the thermostat set point. The hot water then flows from the tank, through the tempering valve, and on to the faucet. If the water is above the tempering valve's set point, the valve will allow cold water to enter and mix with the hot to avoid a user at the faucet from being scalded. Water, the heat collection fluid used with this type of system, is never automatically drained from the heat collection loop. As a result, such a system should never be used where freezing temperatures are to be expected on a regular basis. These systems should be limited to the very southern parts of the U.S. Provisions for manual draining of the system are a must since even the very southern parts of the U.S. can experience a freeze now and then. Recirculation systems have controls that allow the heat circulation pump to turn on to circulate the water through the collectors during freezing conditions. This simply circulates warm water from the water heater tank to the solar collectors, and this keeps the collectors from freezing. This works well as long as there is power to keep the pump running and enough warm water in the water heater tank to last out the freeze spell.

 

 

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This page was last changed on 1-26-2010