Glycol System

7.0 Glycol System

7.1 Description

A typical glycol system as shown Figure C-7 (overleaf), is a heating/cooling system in which an ethylene or propylene glycol-water solution is circulated to fan coil units throughout the building or through heating/cooling coils in an HVAC system in order to provide space heating/cooling without the inherent risk of freeze damage.

The heat source may be converters, fired heaters, or fired boilers; the cooling source is a chiller.

The principal components of these systems include a heating/cooling source, automatic air vents, circulating pumps, flow switch, expansion tank, heat exchangers, a pumping system to introduce the glycol/water solution into the system, safety valves, low-water fuel cut-off controller, by- pass filter with flow element and corrosion coupon rack (coupon rack and corrosion coupon monitoring is not mandatory on these systems). In order to prevent undetected dilution of the glycol concentration in the system, a water make-up connection is not recommended for these systems; however, if a make-up connection is provided, it must contain a water meter, backflow prevention device & pressure regulator.

Note: Glycol systems for emergency generator diesel engines, which utilise diesel automotive grade glycol in accordance with the supplier recommendations, are not included in this Section.

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Pre- Conditioned Water LWCO

Figure C-7: Schematic Diagram of a Typical Glycol System

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Glycol System (cont’d)

7.2 Operation and Maintenance

Industrial grade glycol is composed of ethylene or propylene glycol, a corrosion inhibitor, and water. Note that automotive grade glycol should not be used in commercial or industrial glycol systems because their corrosion inhibitors have a limited useful life and they contain silicates which can foul or plug the system.

If there is a concern that the glycol may be orally consumed, an industrial grade propylene glycol should be used because of its low oral toxicity, otherwise an industrial grade ethylene glycol is the preferred choice. Note: In order to accurately measure the glycol concentration in the system, ethylene and propylene glycol must not be mixed together in the same system.

Since dissolved oxygen in the system will decompose glycol into an organic acid, particularly at elevated temperatures, thus causing corrosion & fouling, both types of glycol contain a corrosion inhibitor, typically dipotassium hydrogen phosphate.

The water which is used to mix with concentrated glycol must be of the highest possible quality (i.e., softened, demineralized, deionized, boiler condensate); otherwise the hardness and corrosive salts in most domestic water supplies will deplete the corrosion inhibitor concentration in the glycol.

Once the system is filled with the glycol-water solution, every effort must

be made to minimise the entrance of additional hardness salts and dissolved oxygen into the system by the operational type methods indicated below.

(a)

A water connection is not recommended; however, if a water connection is provided, limit the amount of make-up water as follows: (i)

install a water meter in the water make-up line, and confirm its operation by noting the changes in its reading before & after such activities as water sampling, low-water fuel cut-off controller blowdown, safety valve testing & filter cartridge replacement activities;

(ii)

locate & repair system leaks immediately;

(iii)

adjust pump seals with packing so that there is minimum leakage;

(iv)

ensure that pumps with mechanical seals have zero leakage;

(v)

do not drain & fill the system seasonally—if maintenance or inspections are required, only those portions of the system that are affected should be drained;

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Glycol System (cont’d)

7.2 Operation and Maintenance (cont’d)

(vi) ensure that safety valves have zero leakage;

(vii) minimize loss from the system during glycol sampling, low- water fuel cut-off controller blowdown, safety valve testing & filter cartridge replacement activities;

(viii) All glycol discharge shall be captured to be re-used or disposed

in accordance with Environmental Guidelines.

(b) Ensure that there is a positive pressure at the top of the system at all times by maintaining a minimum static system pressure according to the following equation by the addition of air to the expansion tank:

Imperial formula: P = (H/2.31) + 5 Metric formula:

P = (9.81 x H) 34.5

Where P:

pressure at the circulating pumps with the pumps shut off, psig or kPa;

H: elevation of the system piping above the circulating pumps,

feet or meters;

(c) Ensure that there is a glycol-water solution level in the expansion tank at all times;

(d)

Replace faulty automatic vents as required;

(e) In order to prevent excessive decomposition of the glycol into organic acids, the operating bulk temperature of the glycol-water solution must

be limited to 120 ° C (250 ° F).

7.3 Chemical Treatment

In order to provide freeze protection (i.e., a glycol concentration which is sufficient to prevent the formation of ice crystals and thus remain pumpable at the lowest temperature experienced by the fluid) down to at least -34 °

C, the acceptable glycol concentration range for cooling systems which are operational year round and for heating systems is 48-87 vol% for ethylene glycol systems and 49 vol% minimum for propylene glycol systems; however, for the economic reasons, the preferred glycol concentration range is 48-52 vol% with a corresponding freeze point range of –34 ° C to –40 ° C for ethylene glycol systems and 50-54 vol% with a corresponding freeze point range of –

34 ° C to –40 ° C for propylene glycol systems. Other than causing a higher energy consumption, a high glycol concentration is acceptable; therefore, dilution is not required, unless the ethylene glycol concentration is greater than

88 vol%. .

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Glycol System (cont’d)

7.3 Chemical Treatment (cont’d)

In order to provide burst protection (i.e., a glycol concentration which is high enough to prevent bursting of pipes and other mechanical damage, but not necessarily high enough to keep the fluid pumpable) down to less than -50

C, the acceptable glycol concentration range for ethylene glycol cooling systems which are operational only during the summer months is 30-85 vol%; however, for economic reasons, the preferred glycol concentration

range is 30-35 vol% with a corresponding freeze point range of –16 ° C to –

C. Similarly, the acceptable propylene glycol concentration range is 35 vol% minimum, but the preferred range is 35-40 vol% with a corresponding freeze point range of –16 ° C to –19 ° C for burst protection down to less than -40 °

C. Other than causing a higher energy consumption, a high glycol concentration is acceptable; therefore, dilution is not required

These lower glycol concentrations are in place only if the glycol system is not exposed to outside temperatures during the winter months.

Since glycol concentrations less than 20 vol% are a nutrient source for bacteria, the glycol concentration must be greater than 20 vol%.

The following equation may be used to calculate the approximate amount of glycol required to increase the glycol concentration in a system:

G = V x (CD-CP)/(100-CP)

Where G: volume of present glycol solution to be drained from the system and volume of fresh concentrated glycol to be added to the system, litres

CD: desired glycol concentration, vol% CP: present glycol concentration, vol% V:

volume of the system, litres

In order to provide adequate corrosion protection of the glycol system, the reserve alkalinity based on a glycol concentration of 100% (i.e., RA 100%), which is an indication of the corrosion inhibitor level, must be maintained at a level of at least 9.0 for all glycol concentrations by corrosion inhibitor additions as required.

If the RA (100%) value is less than 9.0, the following equation may be used to calculate the first estimate for the amount of corrosion inhibitor addition that is required:

I = 1.75 x V/100

Where I:

volume of inhibitor, litres

V: volume of the system, litres

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Glycol Systems (cont’d)

7.4 Control Tests

In order to minimize fouling and/or corrosion of glycol systems, the following control tests must be performed (note that due to the more sophisticated nature of the chemical tests for glycol systems, the glycol concentration, pH & reserve alkalinity levels for glycol samples should be performed by a commercial laboratory. Testing of glycol samples shall be arranged between the Water Treatment Specialist and the Building Operator:

(a) Document the make-up water meter reading at least once per

month—it must be negligible;

(b) Determine & document the glycol concentration in the system at least once per year—the following control limits must be maintained:

(i)

for ethylene glycol cooling systems that are operational year round & for ethylene glycol heating systems, the glycol concentration must be 48-52 vol% with a corresponding freeze temperature of –34 to –40 ° C & a burst temperature of less than –50 ° C;