# Hydroponics pump size- How to calculate pump size

- Posted by Pierre
- Categories Hydroponics

In this section, I will show you exactly how to calculate the correct pump for your hydroponic system. We will discuss the different systems first, and then we’ll do a combined calculation.

## Nutrient film technology (NFT) system

The first system is a nutrient film technology (NFT) system we have got a thin film of water running at the bottom of the pipe, and it circulates thru the system.

There are two things that you must calculate in your pump calculations. The first is the head of your pump. It is calculated from the lowest level that the water can go in your sump up until the highest level that the water is lifted by your pump. This is the total head of this system. We will talk about friction in the pipes just a little bit later. The next thing is your flow rate; your flow rate in an NFT system is typically 10 to 25 L per hour per pipe. It is much slower than for instance, in an aquaponics system, because in a hydroponics system we’ve only got the nutrient solution that we circulate and there’s no nitrification process happening. The slope in an NFT system is 2 to 4%, that equates to 2 to 4 cm per 1 m.

## Vertical grow towers

The next system is vertical grow towers. In the sketch case, we’ve got three vertical grow towers. The head of our pump is from the lowest level in the sump to the highest level that the water must be lifted, and that will give us our head. The flow in these towers is typically 10 to 25 l per hour. So for every single tower, you need to be able to deliver 10 to 25 L. If you go for the lower end and you’ve got three towers then it means if you’ve only got these three towers in your system your total volume that you must shift is then three times that 10 which is 30 litre per hour.

## Deep water culture (DWC)

The next system is our deep water culture with your floating rafts on top. Again your head is calculated from the lowest level that the water can go in your sump, to the highest point that the water must be lifted. The flow rate, in this case, is calculated at least your grow bed volume per hour. If this is a 100 l bed, then your flow rate in this system must be 100 litres per hour.

## Flood and drain system

In a flood drain system, you usually got grow media as part of the total volume of your system. It may be expanded clay pellets, gravel, crushed rock or any type of media. The media take up space in your grow bed and for instance if your grow bed is 200 l it’s not to say it will take 200 l of water. An easy way to do the calculation is to take a 1 l container (by volume), put the grow media in and fill with water, then drain the water out and measure the amount of water in litres. In this way, you can calculate the % that will be water in your system with your specific grow media.

Again your head is calculated from the lowest level that the water can go in your sump, to the highest point that the water must be lifted. The flow rate is calculated as at least your grow bed volume per hour (water not media).

## Example of a combined system

Let’s do a quick example of a combined system (see figure below).

The system consists of the following:

- Three vertical towers
- an NFT system,
- a flood and drain bed,
- a deep water culture bed
- and the sump is 4000 l.

Let’s start with the vertical Towers, there’s three of them, and we selected 20 l as the flow rate per tower per hour. This will give us a total of 60 l per hour for the vertical towers. Then we’ve got the NFT system it’s only one of them in this case at 20 l per hour. Then we’ve got a deep water culture system with a volume of 1000 l and a flood and drain system of 500 l.

In any system, you must calculate the total floor as well as the total head. in the figure above you can see that the total flow in the system is equal to 1580 l per hour. The total head is calculated from the lowest level of the water in the sum up until the highest level that the water must be lifted. in this example, it is 1.8 m. You also have to compensate for the amount of friction loss in the pipes. as a rule of thumb, we add 20% to the head which will give us a total head of 2.16 m. We now have the two main parameters that we need in order for our pump selection we’ve got a flow of 1580 l per hour as well as a head of 2.16 m.

## Pump selection

Let’s consider the two pumps in the graph below. As calculated our desired flow rate is 1580 L per hour, and our total head is 2.16 m. as you can see from the chart we’ve got the head on the vertical axis and the flow rate on the horizontal axis. This is a typical pump Curve that you will use in the selection of a pump. It is supplied by the manufacturer of the pump and is usually printed on the box. It can also be obtained from the internet and pump datasheets.

If we consider the DDF 50 pump which presented in the lower Curve, we can see that at a head of 2 m it can only deliver 1000 litre per hour. the DDF 50 pump will thus not be able to supply the amount of water at the desired head.

Let’s consider it the second pump (DDF 110). At a head of 2 m, it will be able to supply 2000 l per hour, which is more than the calculated 1580 l per hour. If you have a choice, it’s always better to select the pump that can deliver more than the desired amount of litres per hour. This will leave room for future add-ons in your system.

## Types of pumps

There are many types of pumps available and you have to do your research in order to select the best fit for your specific system. I’m just going to mention one or two things that you may consider in the selection of a pump. in the sketch, right below this text, you can see an example of a magnetically coupled impeller pump. Although these pumps are normally quite energy-efficient you will find that the head is normally not sufficient.

In many cases, similar pumps from a specific manufacturer will be plotted on one graph as can be seen below. This will make it easy to select a pump that is a good fit for your system.

It is also important to consider the economy side of the pump. Pumps with built-in variable frequency, drives are becoming more readily available, affordable and are extremely efficient.

Take your time in the selection of your pump and make sure that you get a good quality pump that will give you many years of trouble-free service in your system.

I hope you found some value in this article and that it will help you to select the perfect pump for your system. You are also welcome to check out my YouTube video below regarding pump selection in a hydroponic system.

I also have a very affordable online course on aquaponics and hydroponics systems where we study each of the individual systems. The course consists of more than 50 video lessons where I cover relevant information that will save you a lot of time and heartache in your aquaponics or hydroponics journey. A link to the course can be found on the right-hand side of this page.

I am an electronic engineer with more than 50 scientific publications. My motto is “if you can not explain it simply, then you do not understand it well enough”.