GB2468211A

GB2468211A - Biocide suitable for use as a heat pump flushing solution

Info

Publication number: GB2468211A
Application number: GB201003251A
Authority: GB
Inventors: Robert Gerard Simcox; Alan Marshall
Original assignee: Sentinel Performance Solutions Ltd
Current assignee: Sentinel Performance Solutions Ltd
Priority date: 2009-02-27
Filing date: 2010-02-25
Publication date: 2010-09-01
Anticipated expiration: 2030-02-25
Also published as: GB0904023D0; GB2468211B; GB201003251D0; GB0903394D0

Abstract

A biocide suitable for use as a heat pump flushing solution comprises: 75 to 98 % by weight water, 0.1 to 25% by weight hydroxide peroxide and 0.01 to 10% by weight particulate silver. The biocide is particularly effective for use in ground source heat pumps of the closed-loop or open-loop types. Also claimed is a method of commissioning a ground source heat pump comprising the steps of; flushing the heat pump with water, measuring the bacterial levels instantaneously using a bioluminescence technique and a luminometer, flushing the heat pump with a biocide of the present invention, measuring the bacterial levels again and introducing the thermal fluid into the ground source heat pump ground loop.

Description

HEAT PUMPS

The present invention relates to a method, and a novel biocide formulation, suitable for use in relation to heat pumps such as ground source heat pumps.

Ground source heat pumps use a thermal fluid which acts as a refrigerant fluid when operating in cooling mode or a thermal fluid when operating in heating mode. The thermal fluid is usually propylene glycol, but other glycols such as ethylene glycol may be used, which functions as a heat transfer medium and an anti-freeze.

A major problem encountered with known heat pump installations is that the thermal fluid deteriorates (degrades), and in extreme cases it forms a jelly like material which has increased viscosity and reduced frost protection. The thermal fluid can also have reduced heat transfer capability. The degraded thermal fluid reduces the diameter of the pipe work, the freezing point of the thermal fluid increases, there is a colour change and the viscosity increases. The degradation is usually accompanied by a decrease in pH. The thickening of the fluid and the solid deposits formed cause blockages and the degraded fluid has a reduction in heat transfer capability. The effects on the heat pump are an increase in pumping costs and reduced efficiency. There is also a reduction in protection against frost damage and an increase in down-time to change the thermal fluid. It was thought that the degradation was caused solely by heat but surprisingly it has been found through extensive testing that the main cause is a build up of bacteria from contamination in the pipe (e.g. from bird, rodents or insects) or from soil entering the installation before it is commissioned and/or through small fissures/gaps during use.

The aim of the invention is to overcome these by a novel method of flushing a ground source heat pump ground loop and a novel biocide formulation for use in this method.

There are many biocides that can effectively kill bacteria and fungi and a number of biocides either individually or in combination have been considered for this application. The table below shows the biocides considered for this application: *..* * * S...

S

*..... * S S. * * . . * ...

S S.. * ** * S S * SS, *S S * S* S *S

Potential Biocides for GSHP Ground Loops Typical Comments Suitability Biocidal Rating (3=Good, 0 = Poor) Dosage for a Algae Fungi mgll GSHP Ground Aerobic Anaerobic Loop Actives Bacteria SRB biocide BNPD/ISZ 3 2 2 2 40 to 60 Good on nitrifying bacteria Yes BNPD/DGH 2 3 3 3 30 to 90 DGH is good for sulphate reducing bacteria. Yes Peroxide/Ag 3 2 2 2 100 -Low environmental impact. Very effective against bacteria. Strong on algae and fungi. Fast acting. Oxidising agent. Yes ISZ 3 2 1 1 60 to 80 Good on bacteria (Nitrifiers esp.) Biostatic and persistent action. Too slow for this application. No Glute 2 2 1 2 75 to Low environmental impact Good with Cl2 and Br2, Good with MB and algae, good in alkaline pH No MBT Dithiol 3 1 1 2 50 to Fast acting biocide. Rapid hydrolysis at pH >8.5.

High environmental impact. No BNPD/Quat 2 2 2 1 60 to 80 Low health risk. Good No with Cl2; Good at * , . alkaline pH. Tendency to foam * JNPA 2 1 0 1 20 to 40 Mainly a bactericide, No weak on algae /fungi * UOt/DGH 2 2 2 2 50 to 80 Low environmental -impact;goodonalgae * * especially with Cl2, ** Tendency to foam No * ** __________ _____________ ________ _________ __________ ________________________ _____________ * * * ** * * S S

S

0 0 3 0 50to80 Algistat only.

TBA Synergistic with Cl2 No Phos Quat 2 1 2 1 100 to Possible reduced No Glute 200 efficiency in high hardness waters.

Tendency to foam Quat 2 1 2 2 50 to 80 Low environmental impact, good on algae especially with Cl2.

Tendency to foam. No DGH MBT 3 3 3 3 30 to 60 DGH is good for sulphate reducing bacteria. High environmental impact No Hypochlorite 3 2 1 2 1 to 2 Effective fast acting biocide for bacteria. Cost effective. Can result in corrosion of stainless steel. No Chlorinated 2 1 1 1 1010 Poor effect againstAlgae, phenolic 150 fungi and anaerobic bacteria. No

BIOCIDES

BNPD Bromonitropropanediol Chlorinated phenolic Chlorinated phenolic compounds DBNPA Dibromonitropropionamide DGH Dodecylguanidine hydrochloride Dithiol Dithiol Glute Glutaraldehyde Hypochlorite Sodium Hypochlorite ISZ Isothiazolin * ** M BT Methylenebisthiocyanate fetoxeIAg Hydrogen Peroxide/Silver Powder :1Dhos Quat Phosphonium Quat at ----Quaternáry ammonium compound -- * *"rBA Terbuthylazine * ** * *. ** S * I. * .5

Many of these biocides can be deemed unsuitable for the application in ground source heat pump ground loops on the basis of effectiveness, speed of the killing action, handling characteristics, environmental impact, corrosivity, cost effectiveness, or toxicity to aquatic life and mammals..

According to one aspect of the present invention a biocide suitable for use as a heat pump flushing solution comprises: to 98 % by weight water, 0.1 to 25% by weight hydroxide peroxide and 0.01 to 10% by weight particulate silver.

According to another aspect of the present invention a method of flushing a ground source heat pump ground loop comprises introducing into the ground source heat pump ground loop the following biocide to 98 % by weight water, 0.1 to 25% by weight hydroxide peroxide, and 0.01 to 10 % by weight of particulate silver.

According to yet another aspect of the present invention, a heat pump flushing solution comprises a biocide consisting of: to 98 % by weight water, 0.1 to 25% by weight hydroxide peroxide and 0.01 to 10% by weight particulate silver.

4ccording to yet another aspect of the present invention, a method of commissioning a ground heat pump comprises the steps of: -a; Flushing the heat pump-with water, -- * .1. Measuring the bacterial levels instantaneously using a bioluminescence technique and a luminometer, * SI * S a. * * * S * . c. Flushing the heat pump with a biocide comprising to 98 % by weight water, 0.1 to 25% by weight hydroxide peroxide, and 001 to 10% by weight particulate silver, d. Measuring the bacterial levels instantaneously using a bioluminescence technique and a luminometer and then e. Introducing the thermal fluid into the ground source heat pump ground loop.

Preferably the biocide formulation used in any of the aspects of the invention comprises to 98 % by weight water, 0.1 to 10% by weight hydroxide peroxide, and 0.01 to 5% by weight particulate silver.

Following extensive chemical investigations and testing, a biocide solution has been devised which is surprisingly effective in slowing down the degradation of thermal fluid in ground source heat pumps ground loop, is not corrosive to the material of the heat pump which is usually of stainless steel and copper, is safe for an operative to handle, is of low toxicity to aquatics and animal life and is fast acting. The combination of hydrogen peroxide and silver is much preferred, as it performs better than other biocides such as BNPDIISZ or BNPD/DGH.

There are four basic types of ground loop systems. Three of these-horizontal, vertical, and pond/lake-are closed-loop systems. The fourth type of system is the open-loop option. Which *rie of these is best depends on the climate, soil conditions, available land and local :15tati0n costs at the site. All of these approaches can be used for residential and *: :mmea1 building applications.

S * ** * * * S... S. S S* * *S

Closed-Loop Systems Horizontal This type of installation is generally most cost-effective for residential installations, particularly for new construction where sufficient land is available. It requires trenches at least four feet deep. The most common layouts either use two pipes, one buried at six feet, and the other at four feet, or two pipes placed side-by-side at five feet in the ground in a two-foot wide trench.

The Slinky method of looping pipe allows more pipe in a shorter trench, which cuts down on installation costs and makes horizontal installation possible in areas it would not be with conventional horizontal applications.

Vertical Large commercial buildings and schools often use vertical systems because the land area required for horizontal loops would be prohibitive. Vertical loops are also used where the soil is too shallow for trenching, and they minimize the disturbance to existing landscaping. For a vertical system, holes (approximately four inches in diameter) are drilled about 20 feet apart and 100-400 feet deep. Into these holes go two pipes that are connected at the bottom with a U-bend to form a loop. The vertical loops are connected with horizontal pipe (i.e., manifold), placed in trenches, and connected to the heat pump in the building.

Pond/Lake If the site has an adequate water body, this may be the lowest cost option. A supply line pipe is run underground from the building to the water and coiled into circles at least eight feet under the surface to prevent freezing. The coils are only placed in a water source that meets ***rrinimum volume, depth, and quality criteria.

* .*..* * Open-Loop System (less popular) *. * :-i1 type of system uses well or surface body water as the heat exchange fluid that circulates directly through the OHP system. Once it has circulated through the system, the water returns ::fG the ground through the well, a recharge well, or surface discharge. This option is obviously *:.actica only where there is an adequate supply of relatively clean water, and all local codes and regulations regarding groundwater discharge are met.

Installation Once the ground loop system has been installed either in the trench for horizontal loops or in the borehole for vertical loops the system is flushed with water and pressure tested. There can be a time delay between the pressure testing and when the ground ioop system is filled with a thermal fluid. The thermal fluid is usually a water/glycol based product which is formulated to provide frost protection, corrosion inhibition and heat transfer capability.

The Problem During the storage of the piping used to fabricate the ground loop system it is possible that contamination can occur from birds, rodents or insects and during installation of the ground loop system inevitably soil will enter the piping used to fabricate the ground loop system.

Bacteria are single-celled organisms, and live in the soil, with populations ranging from 100 million to 3 billion in a gram. They are capable of very rapid reproduction by binary fission (dividing into two) in favourable conditions. One bacterium is capable of producing 16 million more in just 24 hours. Bacteria live in soil water, including the film of moisture surrounding soil particles, The bacteria require high soil water content and an easily degradable carbon source (glycol). Certain bacteria require a low level of nitrogen compounds and ideally a soil pH levels are between 6 and 9. Phosphorus compounds are a required by certain bacteria together with low levels of oxygen.

The solution Preferably the flushing procedure for the ground source heat pump ground loop is as follows, using the biocide of the present invention (e.g. Biocide A): S... * . *...

* Nush out the new system with water to remove any debris that may remain from the *:..mbh of the system. *

*Take a sample of water and measure the bacterial levels using the bioluminescence technique.

handhd lumorneterisa sufta1e instrument for the determination of *cteria levels instantaneously. The Lumitester PD1O handheld luminometer is used in conjunction with a swab stick of the LuciPac W which is immersed in the sample of water until saturated. The swab stick is then put back into the main body and pushed to break the capsule in the test tube, permitting the liquid contained in the capsule to flow into the test tube. The whole body of the LuciPac W is shaken several times so that any remaining liquid in the capsule falls into the test tube. The whole body of the LuciPac W is inserted into the measuring chamber of Lumitester PD-I 0. The "ENTER" key is pressed and the results are obtained within 10 seconds. Also take a sample of water from the system and measure the bacterial levels using a dipslide. Using the comparison charts read and record the result after 48 hours storage period.

During the first filling of the new system with water add I litre of Biocide A. For systems larger than 300 litres add I litre per 300 litres, Circulate the system for 30 minutes to allow mixing and distribution of the Biocide A throughout the whole system. Use the test kit and measure the concentration of Biocide A using the test strips. The correct dose will give a reading of lOOppm on the test strips. If the reading is found to be below lOOppm top up the system with Biocide A until a reading of lOOppm is achieved.

Take a sample of water from the system using a swab stick of the LuciPac W and measure the bacterial levels using the Lumitester PD1O handheld luminometer for the determination of bacteria levels instantaneously and also measure the bacterial levels using a dipslide. Using the comparison charts read and record the result after 48 hours storage period.

If the RLU (relative light units) values from Lumitester PD1O handheld luminometer are greater than 0, add additional Biocide A and ensure that the reading is at lOOppm or above. Once the ground source heat pump ground loop has been flushed sufficiently with the biocide the new ftermal fluid can be introduced. As the thermal fluid is pumped into the ground loop, it pushes * otit the flushing water (biocide). S. S

II

S 1.1

Fill the system with thermal fluid and circulate to remove all the entrapped air. Take a sample of :::,erma, fluid from the ground loop using a swab stick of the LuciPac W and measure the *cterial levels using the Lumitester PD1O handheld luminometer and also measure the bacterial levels using a dipslide. Using the comparison charts read and record the result after 48 hours storage period.

At the annual service a dipslide test should be taken to confirm satisfactory bacterial levels.

Examples:

Example 1 -Method

6 horizontal Ground Energy Collectors were filled sequentially with water and circulated to remove any entrapped air in the loops. The bacteria levels were measured after three loops had been filled and the entrapped air eliminated and again after the six loops had been filled and the entrapped air eliminated. The circulating water was then also directed to flow through the heat pump leg of the system and the bacterial levels measured. The bacterial levels were measured on the water flowing through the complete system.

The flow to the heat pump leg of the system was closed off. The flow to the 6 horizontal Ground Energy Collectors was dosed with 2 litres of Biocide A and the system was circulated for 30 minutes. The level of Biocide A was determined and the bacterial levels were also measured.

The circulating water was then also directed to flow through the heat pump leg of the system and the level of Biocide A was determined and the bacterial levels were also measured. The level of Biocide A was determined and bacterial levels were measured on the water flowing through the complete system.

When it had been determined that the system had been sterilised a thermal fluid containing blue dye was introduced into the system. The 6 horizontal Ground Energy Collectors were filled quentia1Iy with Thermal fluid until the point that water being flushed from the loop showed the colouration from the Thermal fluid. When the 6 ioops had been filled the same procedure was used to fill the heat pump leg of the system. The system was circulated to remove any * remaining trapped air and then the bacterial levels were also measured and the concentration 6f propylene glycol determined. * *e * * S 55I*

Techniques Bacteria Determination: Lumitester PD1O Dip Slides Biocide Concentration: Dip Sticks Results Results from the Lumitester PD1O System Fluid 3 loops 6 loops Heat Pump Total System System Leg Water 29 RLU 35 RLU 150 RLU 98 RLU Water with added 4 RLU 5 RLU 4 RLU 4 RLU Biocide A Thermal Fluid 0 RLU 0 RLU 0 RLU 0 RLU Results from Dip Slides * * **** *.* *. * *

*: system Fluid Total System * * Water i03 org/mi : * Water with added S. 5 *:.oc1deA >i03 org/mi Thermal Fluid >i03 org/mi Biocide Concentration System Fluid 3 loops 6 loops Heat Pump Total System System Leg Water with added. 100 ppm 100 ppm 100 ppm 100 ppm Biocide A

Example 2

Method The horizontal Ground Energy Collectors had been filled with water to pressure test the system about 9 months previously and left capped off and fully flooded. The bacteria levels were *jneasured in the water from the number 1 loop. The water in the loop was replaced with fresh :ater and the flow to the Ground Energy Collector loop was dosed with I litre of Biocide A and the system was circulated for 30 minutes. The level of Biocide A was determined and the levels were also measured.

S

: .When it had-been determined that the system hadbeensterilisedaihermaifluidcontaining -- :5..ue dye was introduced into the system. The number 1 horizontal Ground Energy Collector was filled with the thermal fluid until the point that water being flushed from the loop showed the blue colouration from the thermal fluid. When the loop had been filled the system was circulated to remove any remaining trapped air and then the bacterial levels were also measured and the concentration of propylene glycol determined.

Monitoring Techniques Bacteria Determination: Lumitester PD1O Dip Slides Biocide Concentration: Dip Sticks Results Results from the Lumitester PDIO System Fluid Number I Loop Water 19ORLU Water with added 4 RLU Biocide A *:: *lThermal Fluid 0 RLU S.. ** * S

S

* S _____________ * ** S.. *

: *esults.from Dip Slides -*... S* *

S S S.

System Fluid Number 1 Loop Water i05 org/nil Water with added Less than-Biocide A 1 org/mi Thermal Fluid Zero Biocide Concentration System Fluid Number I Loop Water with 100 ppm added Biocide A Biocide A composition: Water-75 -98% Hydrogen Peroxide -0.1 -25% Silver Powder -0.01 -10% s.. * . *

***.** * * S. S * I* * *. S..

I

* _*._ ---------* S S S... S. S * . S S 55

Claims

CLAIMS: 1. A biocide suitable for use as a heat pump flushing solution comprises: to 98 % by weight water, 0.1 to 25% by weight hydroxide peroxide and 0.01 to 10% by weight particulate silver.
2. A biocide according to claim 1 which comprises: to 98 % by weight water, 0.1 to 10% by weight hydroxide peroxide, and 0.01 to 5% by weight particulate silver.
3. A method of flushing a ground source heat pump ground loop comprises introducing into the ground source heat pump ground loop the biocide according to claim 1 or 2.
4. A method of commissioning a ground source heat pump comprises the steps of: a: Flushing the heat pump with water, b. Measuring the bacterial levels instantaneously using a bioluminescence technique and a luminometer, c. Flushing the heat pump with a biocide according to claim 1 or 2 d. Measuring the bacterial levels instantaneously using a bioluminescence technique * * S...and a luminometer and then S..... * *e. Introducing the thermal fluid into the ground source heat pump ground loop. **
5. A biocide suitable for use as a heat pump flushing solution according to claim 1 and * substantiafly as herein described.

*
6. A method of flushing a ground source heat pump ground loop according to claim 1 and substantially as herein described.
7. A method of commissioning a ground source heat pump according to claim 1 and substantially as herein described. * .
S...S S....S S SI * * .. * I* * ** *5S.SS I * . SI SI