National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Water Consumption from 

Freeze Protection Valves for 

Solar Water Heating Systems 

J. Burch and J. Salasovich 

Presented at the ISES Solar World Congress 

Orlando, Florida 

August 6–12, 2005 

Conference Paper 

NREL/CP-550-37696 

December 2005 
NOTICE

The submitted manuscript has been offered by an employee of the Midwest Research Institute (MRI), a 

contractor of the US Government under Contract No. DE-AC36-99GO10337. Accordingly, the US 

Government and MRI retain a nonexclusive royalty-free license to publish or reproduce the published form of 

this contribution, or allow others to do so, for US Government purposes. 

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any 

warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or 

usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not 

infringe privately owned rights. Reference herein to any specific commercial product, process, or service by 

trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, 

recommendation, or favoring by the United States government or any agency thereof. The views and 

opinions of authors expressed herein do not necessarily state or reflect those of the United States 

government or any agency thereof. 

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy 

and its contractors, in paper, from: 

U.S. Department of Energy 

Office of Scientific and Technical Information 

P.O. Box 62 

Oak Ridge, TN 37831-0062 

phone: 865.576.8401 

fax: 865.576.5728 

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from: 

U.S. Department of Commerce 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

phone: 800.553.6847 

fax: 703.605.6900 

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
WATER CONSUMPTION FROM FREEZE PROTECTION VALVES 

FOR SOLAR WATER HEATING SYSTEMS 

Jay Burch 

Jim Salasovich 

National Renewable Energy Laboratory 

1617 Cole Blvd., Golden, CO 80401-3393 

e-mail: jay_burch@nrel.gov 

ABSTRACT 

Freeze protection valves (FPV) have been used in direct 

solar domestic water heating systems (SDWH) in mild 

climates to prevent freeze damage of the collector. Pipe 

freezing in passive systems can also be prevented using 

these valves. A limiting factor on where FPVs might be 

used is the amount of water consumed through use of the 

valve. An experiment was performed to determine the 

average flow rate through FPVs over a range of air and 

water supply temperatures. The experimental flow rate data 

was then used in a simulation to determine the annual flow 

through FPVs for 215 sites throughout the continental 

United States. A correlation between the annual flow and 

the site air-freezing index (AFI) was then developed in order 

to increase the spatial data density to over 3,300 sites using 

AFI data. U.S. maps were generated to display the results 

graphically. The maps show that there is great potential to 

increase the market of direct and passive SDWH by using 

FPV versus using pipe insulation only, although valve 

reliability remains a concern. 

1. INTRODUCTION 

Freeze protection valves (FPV) are also called “freeze 

prevention valves” and “dribble valves.” FPVs can be used 

to freeze-protect piping (1) and solar collectors (2). In the 

state of Florida, direct solar domestic water heating systems 

(SDWH) commonly use an FPV located near the collector 

outlet to protect the collector tubes from freezing during the 

occasional freezing episodes, as in Fig. 1. FPV for collectors 

were studied in (3), including reporting of open/close 

temperatures, fully-open flow rates, and limited reliability 

testing. An FPV can also be used so as to freeze-protect 

supply and return piping, as in Fig. 2 for an indirect 

thermosiphon system. Note that in this case the FPV should 

be located near the ceiling level in the attic, to allow mains 

water to travel through both supply and return piping. In this 

geometry, an FPV could be used to extend the geographical 

market for passive systems, which have pressurized 

supply/return piping in the attic. This would presumably be 

only for passive systems with load-side heat exchangers. 

For passive systems with direct, pressurized storage, FPV 

actuation would purge tank energy and would presumably 

not be advisable. Using FPV for freeze protection of passive 

system piping as in Fig. 2 is somewhat novel in the solar 

field, and is the motivation for the work here. 

Fig. 1. A direct circulation system schematic. The freeze 

prevention valve (FPV) is shown near the collector outlet. 

Continental U.S. maps of pipe freeze probability for passive 

SDWH due to freezing of insulated pipes were published in 

(4). A map of the 20-year freeze probability for attic piping 

freeze-protected with insulation only is shown in Fig. 9. The 

regions with zero or near-zero freeze probability (where 

passive systems can safely be installed) is limited to warmer 

parts of Florida, Arizona, and California. Although it 

appears that FPV manufacturers’ literature places no 

geographical limit on where FPVs can be used, water 

1�
consumption is certainly one limiting factor. The average 

flow rate is affected both by valve geometry (subsumed in 

the fitting factor Cv) and by complex cycling behavior. 

However, data for flow versus temperature conditions are 

not available from manufacturers or from previous studies. 

The goal of this paper is to quantify the loss of water from 

use of FPVs for protecting collectors and/or piping. 

Freeze protection valves operate by using the volume 

change upon freeze of a wax-like material filling a small 

enclosure to open the valve, which allows relatively warm 

supply water to circulate. The valves require no electricity 

to operate. The setpoint temperature (Tset) is the temperature 

at which the valve starts to open, and is determined by the 

wax makeup. Tset is typically chosen to be either 35o

F (for 

protecting pipes) or 45o

F (for protecting collectors). The 

higher setpoint is used for collectors because they can freeze 

above 40o

F, due to infrared flux to the cold sky. The fully 

open position is reached when the effective valve 

temperature drops a few degrees below the setpoint. Table 1 

lists and Figure 3 shows five freeze prevention valves. Note 

that the maximum temperature limit (available for two FPV) 

may be exceeded during stagnation events on active 

collectors. Such events may lead to premature valve failure. 

conditioned space 

DHW Piping 

Must freeze protect 

piping in attic 

Place FPV where 

return piping enters To Drain 

Fig. 2. FPV protecting supply and return piping for an 

indirect thermosiphon system. The valve is placed just 

before piping enters conditioned space. 

The wax-actuator is immersed in the water within the 

piping. When cold ambient temperatures drive the stagnant 

water below the setpoint, the valve begins to open and allow 

water flow. At this point, warmer water from mains will 

flow through the valve, warming the valve (and 

pipes/collector). The valve will then generally modulate 

back to the closed position. An example of this cycling 

behavior is shown in Fig. 5. The time constant and 

dynamics of this cyclic behavior depend on complex heat 

transfer mechanisms, and would be very difficult to predict. 

The specific objectives of this paper are to: i) present 

experimental results for the flow rate through representative 

FPVs as a function of water, ambient, and setpoint 

temperatures; ii) calculate and map annual water 

consumption in solar water heating systems for continental 

U.S. locations. 

TABLE 1: FREEZE PROTECTION VALVE SPECS 

Freeze Prevention 

Valve Manufacturer Model Maximum Pressure 

Maximum 

Temperature 

Set Point 

Temperature 

(psi) (F) (F) 

Dole/Eaton FP - 45 150 45 

Dole/Eaton FP - 35 150 35 

Therm-Omega-Tech IC/FP - 35 100 200 35 

Ogontz F 35 BDT 200 35 

ProFlo V243T 150 200 35 

Fig. 3: Five freeze protection valves. From left to right: 

Dole/Eaton FP-45, Dole/Eaton FP-35, Therm-Omega-Tech 

IC/FP-35, Ogontz F 35 BDT, and ProFlo V243T. Only the 

first three were tested. 

2. FREEZE PROTECTION VALVE EXPERIMENT 

An experiment was set up to measure the average flow rate 

through an FPV as a function of water and ambient 

temperatures. A schematic diagram of the experiment is 

given in Fig. 4. A freezer was used to create a cold air 

temperature environment for the FPVs. The temperature 

range of the freezer is 0 to -40 o

C, and the deviation from 

setpoint is ~1 o

C. The freezer is equipped with an internal 

fan to promote an even temperature distribution. The 

internal dimensions of the freezer are 19x49x17 inches and 

there are four 1-inch diameter ports on the two 19x17-inch 

sides of the freezer. The ports allow water to be piped to the 

FPVs inside the freezer and sensors to be routed inside of 

the freezer. Originally, copper was used for piping from 

outside the freezer to the FPV. However, conduction caused 

an unacceptable upward bias to valve temperature; valves 

would not open when freezer temperature was significantly 

below setpoint. To eliminate this bias, a section of Tygon 

tubing was rolled up and placed between the copper pipe 

from outside and the FPV, as shown in Fig. 4. 

2�
3

A circulator was used to supply constant-temperature water 

to the FPVs. The circulator is capable of chilling or heating 

the reservoir fluid to a desired setpoint in the range -15 o

C to 

+35 o

C. The circulator is equipped with a positive 

displacement pump that is capable of supplying a flow rate 

of 3.0 GPM at a maximum pressure of 60 psi. The halfgallon reservoir of the circulator is open to atmosphere. The 

circulator is placed below the freezer so that the return line 

from the FPV could be open to atmospheric pressure and 

drain to the circulator’s reservoir under gravity. 

Freezer

Freeze 

prevention 

valve

Flow meter Thermocouple

Pressure

transducer

Pressure

regulator

Copper pipe

Circulator

T AV

T

T

T

T

PT PR

FM

BV

Air vent

Ball valves

Swing

valve

Bypass

valve

Check

valve

T

N/C solenoid

valve

T

Tygon tubing

Second Floor

First Floor

Fig. 4: Schematic diagram of the FPV experiment. 

A nutating disc, positive displacement flow meter was used 

to measure the water flow rate through the FPV. The flow 

meter’s electronic transmitter has a pulse output of 0.0418 

gal/pulse, preventing detailed examination of flow during 

the open-close cycle. The typical operating range of the 

meter is listed as 0.5 to 25 GPM, with a maximum error of 

1.5% in that range. Accuracy of the flow meter was checked 

by a “bucket test.” The relatively-inexpensive meter met 

error specification, although the error increased to ~-7% 

(underestimate) at ~.08 gpm. 

A pressure regulator was installed to dampen out any spikes 

in pressure on the supply side of the FPV, and was set to 40 

psi. A bypass valve was used on the supply side just outside 

the freezer to allow for water circulation in the piping when 

a FPV is closed. This was done to prevent damage to the 

pump related to deadheading and to condition the water 

supply piping (so that the temperature set at the circulator is 

the same temperature that the FPV will sense when it 

opens). A swing valve was installed just outside the freezer 

on the polymer drain line from the FPV. This was done to 

stop the natural convection of air up the drain line, which is 

open to atmosphere and could also affect the temperature 

that the FPV is sensing. 

A typical profile of flow versus time is shown in Fig. 5. The 

cycling behavior is evident. Quasi-steady behavior sets in 

quickly, and flow rate is averaged over at least 10 cycles. At 

the highest temperatures, cycle time could be larger than an 

hour, requiring lengthy test duration. Flow rate data were 

collected for a matrix of freezer and water supply 

temperatures intended to correspond to the range of ambient 

air and water mains temperatures where an FPV might be 

used. The nominal matrix of temperatures is 0, -10, and -20 

o

C for the freezer temperature and 5, 10, 15, and 25 oC for 

the water supply temperature. An additional freezer 

temperature of 5 o

C was tested for the FP-45 valve since it 

starts to open at a higher temperature. These are nominal 

setpoint temperatures and the actual temperatures recorded 

during testing were somewhat different; data are reported 

with actual temperature averages during the test. Three of 

the five valves shown in Fig. 3 were tested: the Dole/Eaton 

FP-45, the Dole/Eaton FP-35, and the Therm-Omega-Tech

IC/FP-35. This was done because the two valves tested with 

Tset = 35 o

F yielded very similar results, and it was felt 

unnecessary to test other 35 F valves to roughly characterize 

water consumption. The flow rate data for the three tested 

valves are given in Tables 2 to 4. The flow rates are results 

at 40 psi water mains pressure. Extrapolation to other 

pressures would depend on details of the flow circuits. 

However, neglecting pressure drop down the piping (a good 

assumption for the experiment), flow at other mains 

pressures would be estimated by Eqn. 1: 

test testuse use mPPm. .

= */ (1) 

Flow Rate

Frz = -20C, Wtr = 25C

0

0.01

0.02

0.03

0.04

0.05

13:00 14:00 15:00

Time (Hr:Min)

Flow Rate (gpm)

Fig. 5. Flow rate versus time for the Eaton/Dole FP35 valve. 

Data were stored in one minute intervals. The valve cycled 

on about every four minutes, although cycles can be missed 

due to flow meter pulse resolution. 

As expected, as the freezer and water temperature are 

lowered, the flow rate increases. The flow rates are 

comparable for the FP-35 and the IC/FP-35, with both 

valves having the same setpoints of ~35 o

F. The flow rates 

for the FP-45 are considerably higher at a given condition, 

since it opens at a higher temperature of 45 o

F. 
4

3. FPV SIMULATION AND CORRELATION

The experimental data that relates FPV flow rate as a 

function of freezer and water supply temperature was used 

to simulate the annual flow through a valve installed in a 

solar water heating application. The well-known software 

tool TRNSYS (5) was used for the simulations. The 

simulation uses hourly time steps, and linearly interpolates 

within the flow-rate matrices to obtain the flow. The data 

interpolation routines imbedded in standard TRNSYS were 

used for the interpolation. The simulation is carried out for 

one year using Typical Meteorological Year (TMY2) 

weather data (6). Mains water temperature was derived from 

air-temperature data using the algorithm laid out in (7). A 

total of 215 sites throughout the continental United States 

were simulated in order to obtain the total annual flow 

through the three tested FPVs. 

TABLE 2: FLOW (GPM), EATON/DOLE FP-45.

Freezer Temperature (oC)

-17.3 -8.4 0.6 4.9

5.3 0.965 0.951 0.967 0.962

9.5 0.305 0.184 0.072 0.031

14.8 0.053 0.031 0.014 0.0062

24.2 0.023 0.011 0.0055 0.0019

Water 

Temperatur

e (oC)

TABLE 3: FLOW (GPM), EATON/DOLE FP-35

Freezer Temperature (oC)

-18.9 -9.3 -0.3

6.6 0.0883 0.0393 0.0043

10.7 0.0360 0.0192 0.0030

15.5 0.0199 0.0063 0.0014

24.5 0.0090 0.0052 0.00088

Water 

Temperatur

e (oC)

TABLE 4: FLOW, THERM-OMEGA-TECH IC/FP-35

Freezer Temperature (oC)

-18.6 -9.4 -0.6

4.6 0.113 0.098 0.014

10.8 0.033 0.013 0.0029

15.6 0.016 0.0063 0.0012

24.8 0.0049 0.0019 0.00031

Water 

Temperatur

e (oC)

Correlations to the annual flow data for the three valves 

simulated were carried out using the air-freezing index 

(AFI). AFI is defined as: 

+

=

= ∑( − )

365

1

,

i

freeze TTAFI iday (2) 

where Tday,i is the average air temperature on Julian day i, 

Tfreeze is the freezing point of water, and the + sign indicates 

only positive values are summed. AFI is essentially degreedays to base Tfreeze. The AFI data set used contains AFI data 

at over 3,300 sites in the continental United States (8). This 

increases data density by over 15 times. An empirical 

correlation form was arbitrarily chosen: 

2

swater 1, s 2 AFIaAFIaV s ∗+∗= (3) 

where Vwater,s is the annual water consumption through the 

valve at site s, AFIs is the air-freeze-index at site s, and ai

are regression constants. The TMY2-based simulation data 

set was used to regress the values ai. Eqn. 2 was then used to 

extend the Vwater,s results to the entire NCDC data set 

without simulation. Correlation results are shown in Fig. 6 

for one FPV. The correlation provided a good fit to the 

simulation data, with R2 ≅ 0.97. The fit for the Dole/Eaton 

FP45 valve was not as good, having R2 ≅ 0.67. It is believed 

that degree-days to base Tset (i.e. 35 o

F or 45 oF) would 

provide a better correlation variable than the AFI at base 32

o

F. However, variable-base data that would be needed for 

such analysis are not available, and the extra precision does 

not justify the expense to develop such data. 

Annual Flow vs Air Freeze Index

Dole35 Freeze Protection Valve

y = 0.0014x2 + 1.7748x

R2

 = 0.9712

0

500

1000

1500

2000

2500

3000

0 200 400 600 800 1000 1200

Air Freezing Index

Flow (gal/yr)

Fig. 6. Correlation between annual flow of consumed water 

(y) and the Air Freezing Index (x). 

4. RESULTS

Maps of the continental United States that show the annual 

flow through three FPVs were generated using the results 

from the correlation on the NCDC AFI data. Annual flow 

maps for the Eaton/Dole FP-45 and FP-35 valves are given 

in Fig. 7 and Fig. 8, respectively. The map for the ThermOmega-Tech IC/FP-35 is nearly identical to the Eaton/Dole 

FP35, and is not shown. The FP-45 valve loses considerably 

more water than the FP-35, as expected, since it opens at a 

higher temperature. 

There is no clear-cut answer to the question where to draw 

the “Mason-Dixon line” between an acceptable and 

unacceptable amount of water consumed. Considerations 

include long-term water availability, climate, likelihood of 

drought, and local codes restricting water use. Water 

consumption here should be considered relative to monthly 
5

average water consumption in U.S. homes of 12 kGal/month 

(9). Even though boundaries of FPV use are not definitive, 

the water-consumption maps clearly indicate that there is 

great potential to increase the market of solar water heating 

systems by using these valves, as in the example of the next 

paragraph. 

Let us assume for purposes here an acceptable boundary is 

defined by flows less than 1000 gal/yr. By examining Fig.8, 

the resulting “FPV Mason-Dixon Line” for that valve would 

extend across the U.S. at about the 40th parallel, excepting 

the higher mountains and extending further north yet along 

the coasts. This should be contrasted to the domain where 

passive systems can be safely installed using only insulated 

piping, as shown in one case in Fig. 9. The “pipe-insulation 

Mason-Dixon Line” is limited to parts of Florida, Arizona, 

and California. If an FPV were used as in Fig. 2, the passive 

system domain would be extended by several orders of 

magnitude. Note it is assumed here that the rest of the 

system would not freeze. Although this would be true for 

indirect thermosiphons at any continental U.S. location, it is 

uncertain where ICS collectors (even with their large 

thermal mass) will begin to suffer freeze damage. 

With freeze-intolerant piping (such as copper), FPV for pipe 

freeze protection may not be reliable enough to be used as 

the sole mechanism of freeze protection. The one study we 

have found to date on FPV reliability tabulated SDWH 

damage after a severe freeze in Florida (10). This report 

indicated that about 25% of wax-based FPV failed in that 

event, although an unknown fraction of these failures was 

due to improper installation. A gas-driven mechanism 

(apparently no longer on the market) was said to have much 

lower failure rates (10). Pipe freeze protection is a critical 

need, as one incident can cause damages far in excess of 

system life-cycle savings. It thus is prudent that freeze 

protection of piping should be “multi-leveled,” such that 

failure of the dominant freeze-protection mechanism (e.g., 

FPV) should not lead to burst pipes. For example, one 

might promote use the FPV in combination with use of 

freeze-tolerant polymer piping (such as PEX, as in (11)). 

Other possible freeze protection mechanisms that could be 

additionally employed in a multi-level approach include 

devising buoyancy-driven heat circulation loops in piping 

(12) and using heat tape. 

5. CONCLUSIONS

The average flow rates of three FPVs were measured over a 

range of ambient air and water supply temperatures. Using 

TMY2 weather, the flow rate data were used to simulate the 

annual water consumption of the FPV. A correlation 

between the annual flow and the air-freezing index was 

developed, to use the NCDC AFI data and increase the 

spatial data density to over 3,300 sites. Maps of the 

continental U.S. showing the annual water consumption 

were generated. Annual water consumption is one input 

helping define the regions of the United States where it 

might be acceptable to install FPVs. The results indicate 

there is significant potential to increase the market of 

passive and direct solar water heating systems by using 

FPVs. However, failure data dictate caution, and FPVs 

should not be used as the sole protection mechanism, 

especially for copper pipes where failure of the freeze 

protection can be disastrous. 

6. ACKNOWLEDGMENTS

The authors acknowledge the funding and support of Tex 

Wilkins, the Department of Energy Solar Heating and 

Lighting subprogram manager. Doug Powell and Keith 

Dahlke provided invaluable assistance in carrying out the 

experiments. 

7. REFERENCES

1. Pipe-freeze protection using FPVs is described at: 

http://www.ogontz.com/products/freezeprotection.htm 

2. Standard OG-300 Operating Guidelines and Minimum 

Standards for Certifying Solar Water Heating Systems. 

Available at http://solar-rating.org/standards/ogdocuments/

OG300SEP02.pdf

3. Tiedemann, T., “A Study of Freeze Protection Valves for 

Solar Collectors”, Florida Solar Energy Center, Cocoa 

Beach, FL 

4. Salasovich, J., Burch, J., and Barker, G., “Pipe Freeze 

Probability for Passive-solar Water Heating Systems in the 

United States”, Proc. ASES 2004, ASES, Boulder, CO 

5. TRNSYS description and other information can be found 

at http://sel.me.wisc.edu/trnsys/default.htm

6. Marion, W. and Urban, K., “User’s Manual for TMY2s”, 

available at http://rredc.nrel.gov/solar/pubs/tmy2/

7. Hendron, B., “Building America Research Benchmark 

Definition.” Available at: http://www.eere.energy.gov/

buildings/building_america/pa_resources.html

8. NCDC data products, including the AFI data set, are 

available at http://www.ncdc.noaa.gov/oa/ncdc.html 

9. P. Mayer, et. al., “Residential End Uses of Water,” ISBN 

1-58321-016-4; Cat. No. 90781, AWWA, Denver, CO 

10. Stutzman, G., “Survey of the Solar Industry after the 

December 1983 Freeze,” FSEC-RM-15-85, Florida Solar 

Energy Center, Cocoa Beach, FL 

11. Heater, M., and Burch, J., “Freeze Tolerance of PEX 

Piping,” to be published ASES 2006 

12. Darbaheshti, M., Burch, J., Gawlik, K., and Johnson, T., 

“Freeze Protection for Potable Water Piping Using Natural 

Convection Loops,” Proc. ASES 1999, ASES, Boulder, CO 
 0 to 1E-007

 1E-007 to 10

 10 to 100

 100 to 1000

 1000 to 20000

Flow = 0

0 < Flow < 100

100 < Flow < 1000

1000< Flow < 10000

Flow >10000

 0 to 1E-007

 1E-007 to 10

 10 to 100

 100 to 1000

 1000 to 20000

0 to 1E-007

1E-007 to 10

10 to 100

 100 to 1000

 1000 to 20000

Flow = 0

0 < Flow < 10

10< Flow < 100

100 < Flow < 1000

Flow >1000 

0 to 1E-007

1E-007 to 10

10 to 100

 100 to 1000

 1000 to 20000

Flow = 0

0 < Flow < 10

10< Flow < 100

100 < Flow < 1000

Flow >1000 

0 to 1E-007

1E-007 to 10

10 to 100

 100 to 1000

 1000 to 20000

6 

Fig. 7: Flow (gallons/year) through the Eaton/Dole FP-45 freeze prevention valve. This valve would be chosen for freezeprotecting solar collectors. 

Fig. 8: Flow (gallons/year) through an Eaton/Dole FP-35 pipe freeze prevention valve. This valve would be chosen for 

freeze-protection of piping in the attic. The 1000 gal/yr border might be a reasonable cutoff for use of FPV. 

Fig. 9: Probability of at least one freeze in 20 years, for mild climate states, 3/4” pipe with 1” insulation. The dark dots 

indicate regions where it would be safe to install passive systems with insulated pipes in the attic. The region is quite small, 

and corresponds to where passive ICS are installed today. The region could be extended by using FPVs for pipe freeze 

protection, although reliability concerns demand multi-leveled, fail-safe protection for such a critical function. 

Flow = 0 

0 < Flow < 100 

100 < Flow < 1000 

1000< Flow < 10000 

Flow >10000 

Fl

Flow = 0 

0 < Flow < 10 

10< Flow < 100 

100 < Flow < 1000 

ow >1000 

= 0 

(%) 

> 10 to 100 

> 0 to 1 

> 1 to 10 

Freeze 

Probability 

Pipe Dia. = 3⁄4” 

Insulation = 1” 
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondents 

should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a 

currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

December 2005 

2. REPORT TYPE

Conference Paper 

3. DATES COVERED (From - To)

 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Water Consumption from Freeze Protection Valves for Solar Water 

Heating Systems 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/CP-550-37696 

5e. TASK NUMBER

SH06.5001 

6. AUTHOR(S)

J. Burch and J. Salasovich 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

NREL/CP-550-37696 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

Conference paper regarding research in the use of freeze protection valves for solar domestic water heating systems 

in cold climates. 

15. SUBJECT TERMS

solar domestic water heating; solar water heating; cold-climate solar domestic water heating; cold-climate solar water 

heating 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

17. LIMITATION 

OF ABSTRACT

UL 

18. NUMBER 

OF PAGES 

19b. TELEPONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18