Geothermal Loopfield Flush Cart

Dan Frawley

Dan Frawley

The use of a geothermal flush cart is the last and most important part of any geothermal loopfield installation.  The geothermal flush cart allows you to purge the loopfield of debris and to  fill the loopfield with a glycol/water solution.

Improper purging and filling of a loopfield could result in poor performance or significant damage to your geothermal heat pump.  It’s important that you have the proper equipment.

Purchase or rent your flush cart?

We recommend that you purchase your own flush cart.  As a contractor or certified geothermal installer, it makes good business sense to own a geothermal flush cart.  Renting a flush cart for each project would cost you more in the long term than purchasing a flush cart outright.

Let’s say, hypothetically, that this is your first geothermal project as a certified installer or you are a do-it-yourselfer installing your own system.  As this is your first job you may not have the capital resources to invest in a flush cart right away, or if this is the only project you plan on doing it may not make sense to purchase a flush cart if you’re only going to use it once.

Now some people will tell you that you have to buy a flush cart.  And they would be right as nothing beats purchasing a unit that is specifically designed to do what you need it to do.  But lets be realistic, that doesn’t always make sense especially in economic times that are as difficult as today.

If you don’t buy a flush cart, what can you do?

To answer that, a flush cart is essentially a pump that circulates fluid through the loop field purging all debris, filling it with fluid and pressurizing the whole system.  So if you step back, you probably have everything you need to make your own flush cart sitting around your house.

1) The first part of the flush cart that you’re going to need is a container to hold the fluid that you will be filling the system with.  A 55-gallon drum works great.  A plastic container is preferred as it allows you to see the level of the fluid inside the container.

2)The next part, and most important, is the pump part of the flush cart.   The optimal specifications for the pump is 45 GPM @ 50 ft of head.  The ideal pump is a 2hp electric pump with a maximum flow of 145GPM.  Since pump models vary, check the pump performance chart that will be provided with it.  You can use a gas powered pump, but it is important to note that you will need longer hoses.

You will need to add fireman fittings on to the hoses matching those on your pump panel.  Hook one end onto the top of the barrel to discharge.  Another hose goes from the bottom of the barrel to the pump and then connect the pump to the other fitting on the pump panel.  Mix water with the propylene glycol that you purchased with your geothermal loop field.  The proper ratio is 25/75 fluid to water solution; in other words 25 parts glycol to 75 parts water.

Geothermal Flush Cart

Geothermal Flush Cart

Pump in the fluid and push all the air into the top of barrel.  It is important to keep the fluid in the barrel from becoming aerated to keep air out of the loop field. You can accomplish this by using a section of screen rolled into a funnel.  Keep circulating the fluid until there are no more bubbles, making sure you send fluid through the geo unit as well.  When this step is complete, you can shut of the discharge and allow the pressure to build up before you shut off the flush cart completely.

Once you have completed this process you have successfully purged the loop field of air and debris, filled the system with the glycol solution and pressurized the system.  If all your connections are secure you are ready to backfill the loop field.  Using equipment you most likely have at home you were able to successfully purge and fill your loop field.  It is important to take the time to do this, as air in the system will cause corrosion of the heat exchanger, sacrificing efficiency and performance.  Debris will clog the pump pack, damaging the pumping mechanism and potentially the mechanical parts of your heat pump.

It is always recommended that you purchase a flush cart to install a geothermal loopfield but sometimes that just isn’t practical.  You can create a flush cart that will function just as well from equipment that you already have.

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