In the previous article we have discussed about the solar heating close loop system basics and heat exchanger. In close loop system heat exchanger is the main component that is used to transfer the solar heat energy from solar collector to our home’s hot water system.

To give a clearer picture please check the diagram below, how the heat exchanger works within the close loop.

Previous articles:

1. Choosing the Right Solar Heating- Passive, Active & Open Loop (Part 1)
2. Choosing the Right Solar Heating- ICS & Close Loop Basics (Part 2)

Antifreeze in Solar Heating System

Air or antifreeze is the medium that is circulated within the loop. Normally ethanol, methanol,   propylene glycol and ethylene glycol is used as the medium. Antifreeze is used as freeze protection, to avoid water become ice which is occurred in open loop systems.  In the previous article, we didn’t discuss deeply about this issues.

Although some people might think that this information is only important to engineers or technician, however knowing about chemical properties of the media give you peace of mind.

It is very important to have a basic understanding so that when you go out for solar system shopping, you know what you want to buy. In addition, this is also good information for readers who would like to make their own system or a DIY system in the future.

Ethanol	Methanol
low corrosivenesshigh flammability if purelow toxicity high heat transfer capacity low viscosity moderate cost	low corrosivenesshigh flammability if purehigh toxicity high heat transfer capacity low viscosity low cost

Propylene Glycol	Ethylene Glycol
low corrosivenesslow flammabilitylow toxicity high heat transfer capacity higher viscosity high cost	low corrosivenesslow flammabilityhigh toxicity lower heat transfer capacity higher viscosity high cost

Viscosity

Lower viscosity is better so that the movement of the liquid medium is faster and more efficient to distribute heat energy from solar collector to our home.

Heat Transfer Capacity

Higher heat transfer capacity definitely is the best because more heat energy could be transferred to our home.

Water has the highest heat transfer as well as the highest viscosity comparing any of the antifreezes. However, during winter especially at night water could not be used as it would turn to ice. Antifreeze which is mixed with water is used instead.

Flash Point & Boiling Point

Flash point and boiling point are also important to know since antifreeze has maximum limit of temperature could work. If water has boiling point of 100 degree Celsius then antifreezes have different maximum limits.

Flash point is the lowest temperature where it will evaporate enough fluid to form a combustible concentration of gas. The flash point is an indication of limit that a chemical can burn.

Boiling point is the maximum temperature for the chemical before it evaporates.

Antifreezes Chemical Properties

Ethanol

Freezing Point of Ethanol + Water Solutions

Freezing Point
Ethanol Concentration(% by volume)		0	10	20	30	40	50	60	70	80	90	100
Temperature	(oF)	32	25	15	5	-10	-25	-35	-55	-75	-110	-175
	(oC)	0	-4	-9	-15	-23	-32	-37	-48	-59	-73	-115

Flash Points of Ethanol + Water Solutions

Flash Point
Ethanol Concentration(% by volume)		5	10	20	30	40	50	60	70	80	90	96
Temperature	(oF)	144	120	97	84	79	75	72	70	68	63	63
	(oC)	62	49	36	29	26	24	22	21	20	17	17

Warning: HIGH flammability if pure

Methanol

Freezing Point of Methanol + Water Solutions

Freezing Point
Methanol Concentration(%)	by mass	0	10	20	30	40	50	60	70	80	90	100
	by volume	0	13	24	35	46	56	66	75	83	92	100
Temperature	oF	32	20	0	-15	-40	-65	-95	-215	-225	-230	-145
	oC	0	-7	-18	-26	-40	-54	-71	<-73	<-73	<-73	<-73

Flash Points of Methanol + Water Solutions

Flash Point
Methanol Concentration(%)	by mass	0	10	20	30	40	50	60	70	80	90	100
	by volume	0	13	24	35	46	56	66	75	83	92	100
Temperature	oF	-	130	110	95	85	75	70	60	54	54	54
	oC	-	54	43	35	29	24	21	16	12	12	12

Warning: HIGH flammability if pure and HIGH toxicity

Propylene Glycol

Freezing Point of Propylene Glycol + Water Solutions

Freezing Point
Propylene Glycol Solution(%)	by mass	0	10	20	30	40	50	60
	by volume	0	10	19	29	40	50	60
Temperature	oF	32	26	18	7	-8	-29	-55
	oC	0	-3	-8	-14	-22	-34	-48

Because of slush creation, propylene glycol and water solutions should not be used close to the freezing points.

Boiling Points of Propylene Glycol + Water Solutions

Boiling Point
Propylene Glycol Solution(%)	by mass	0	10	20	30	40	50	60
	by volume	0	10	20	29	40	50	60
Temperature (oF)		212	212	213	216	219	222	225

• T(^oC) = 5/9[T(^oF) - 32]

Ethylene Glycol

Freezing Point of Ethylene Glycol + Water Solutions

Freezing Point
Ethylene Glycol Solution (% by volume)		0	10	20	30	40	50	60
Temperature	(oF)	32	23	14	2	-13	-36	-70
	(oC)	0	-3	-8	-16	-25	-37	-55

Because of slush creation, propylene glycol and water solutions should not be used close to the freezing points.

Boiling Points Ethylene Glycol + Water Solutions

Boiling Point
Ethylene Glycol Solution (% by volume)		0	10	20	30	40	50	60	70	80	90	100
Temperature	(oF)	212	214	216	220	220	225	232	245	260	288	386
	(oC)	100	101.1	102.2	104.4	104.4	107.2	111.1	118	127	142	197

In the next article we shall read more on few types of solar collectors, how it works and some specifications of them. It shall be more interesting article because it is more mechanics than numbers like this article.

Although this article has so many numbers and may be boring, one day you might find it useful as reference when you are shopping for solar heating system. For readers who are interested to know about solar PV and want to get free quotes from the simply visit, FREE SOLAR QUOTES. Thanks for reading.