Garage dehumidifier running costs and energy usage

This is because uncontrolled humidity and your car do not mix well, and when the concentration of moisture in the air is particularly high, your car begins to suffer and will eventually present signs of humidity damage.

Signs of humidity damage include:

• Corrosion and rusting metal
• Mould and mildew in interiors
• Rubber degradation
• Dry and cracked leather interiors

These symptoms come from a single cause: a Relative Humidity (RH) that sits outside 40-60%RH.

What is relative humidity?

In simple terms, RH is simply a measure of moisture concentration in the air relative to the temperature. When vapour in the air comes into contact with surfaces that are coolers than the air itself, it will condense, making your car a prime target.

The speed at which this is likely to happen depends on where you live in the world. For example, if you live in the UK, where temperatures regularly fluctuate, and the average RH sits at around 80%RH, your car is particularly vulnerable to condensation causing rust and mould.

If you live in a dry climate with a low average RH, it will be dry and cracked leather interiors that are your primary concern.

To get rid of this problem, your garage will require a dehumidifier to regulate your car’s environment year-round. But running a dehumidifying system 24/7 isn’t free. While it will save you the cost of having to pay for maintenance and repairs as a result of humidity damage, some solutions are more cost-effective than others.

Calculating the cost of running

There are a number of common solutions used by car owners to stop corrosion in its tracks, but when you’re paying to keep your solution running, it’s important to choose the right option.

For the purpose of this article, we will compare three different forms of treating humidity, including:

• Desiccant dehumidification
• Refrigerant dehumidification
• Heating the garage

Some are more effective and cost-effective than others. Let’s take a closer look.

Let’s compare energy usage and what that means for running costs

For a fair comparison of energy usage, we have used the average UK temperature (14 degrees Celsius) and the average UK relative humidity (80%RH) to work out the cost-effectiveness (and energy-efficiency) of each solution.

At this temperature and RH, the water content sits at 7.98 grams per kilogram.

The calculated energy usage and cost will be based on each solution maintaining 40%RH, the optimum RH for your car, in an average 4-car brick garage space (6m x 12m).

Heating

When it comes to RH, warmer temperatures have a higher capacity to hold moisture. Therefore, if the temperature is maintained (and there are no cool surfaces), there will be less chance for condensation to form. As a result, we’ve seen some car owners use heating in an attempt to stop condensation.

In order to achieve 40%RH from an environment that has 80%RH at 14 degrees Celsius, the internal space of the garage would need to be consistently heated at 25 degrees Celsius. This is a temperature most car owners wouldn’t dream of storing their pride and joy in. However, to achieve an optimum RH in the UK through heating, this is the temperature you’d have to keep up.

The reason the temperature needs to be so high is to account for:

• air infiltration- the unintentional introduction of outside air into your environment
• heat transfer- thermal energy exchange as a result of differing temperature

When the resultant heat loss and total energy requirements are accounted for, heating the garage would take 6.037kW per hour.

If the cost of electricity is 12p per hour and the exact conditions laid out were maintained year-round (heating your garage at 25 degrees and counteracting the outside temperature of 14 degrees), it would cost £6346 annually.

This is a pretty large energy bill. Not only that, but heating damp air is far less efficient that heating dry air, and so when you heat moisture-laden air in order to increase its capacity to hold vapour, you’re fighting a losing battle.

Ultimately, using heating as a solution to maintain the optimum conditions for your car is ineffective, inefficient, and incredibly expensive.

Refrigerant dehumidification

Refrigerant dehumidifiers are the most commonly used dehumidification systems in domestic settings. In order to work, the system uses cold surface coils, which are around 6 degrees celsius.

However, if the surroundings too cool, moisture won’t be able to condense onto the coils. This means refrigerant models are ineffective at lower temperatures. To ensure the refrigerant system does work and maintains the garage at 40%RH, the environment would have to be held at 20 degrees celsius.

If you were heating your garage to maintain 20 degrees celsius as well as running a refrigerant dehumidifier around the clock, accounting for air infiltration, heat transfer, and the volume of water that needs removing, you would require 4.877kW of energy per hour.

But what does this cost if you were to run your refrigerant dehumidifier 24/7 for a whole year?

According to our calculations, (4.877 x 0.12) x 8760- the number of hours in a year, the cost would reach £5126.70, a slightly cheaper alternative to simply heating the space.

But this is still a lot to pay on an annual basis, and bearing in mind how much it would cost to repair humidity damage every few years, a refrigerant dehumidifier is not the most cost-effective option, especially if you experience cooler climates.

Desiccant dehumidification

Desiccant dehumidifier units use regenerative synthetic absorbents to remove water vapour from your surroundings. As the unit draws in air, the absorbents produce a physical change-of-state, dislocating the hydrogen and oxygen molecules to lower the vapour concentration.

Unlike refrigerant dehumidifiers, which are better suited to domestic spaces, desiccant dehumidifiers are able to do their job in even sub-zero temperatures, removing moisture from the air at temperatures as low as -40 degrees celsius. This means they are, by default, better suited to garage environments.

From the get-go, you will not require any additional heating to maintain your garage environment in optimum conditions, and running costs are immediately slashed down.

Based on our Protect desiccant dehumidifiers, in order to remove the volume of vapour in an enclosed 14 degree celsius garage, and maintain it at 40%RH (when the external environment has 80%RH), you will need just 1.51kW.

The cost of running the dehumidifier for 24 hours a day for a full year would be £1587.31, costing significantly less than heating or refrigerant solutions.

However, using a Protect desiccant dehumidifier to enhance the preservation of your car could cost even less than that. Because your car only needs to be maintained in 40-60%RH, when the unit reaches the lower end of the window, it will automatically shut down before switching back on as it approaches 60%RH, using less energy in the process.

Read more about the running costs of a Protect by Dehum car system by clicking here.