Bad idea to use a too big heat exchanger?

[TSN79]

I'm constructing a water based central heating system, and in it is a plate heat exchanger. People often tell me not to be scrimpy regarding its effect when picking one. But then I've heard others say that having a 150 kW heat exchanger - when the effect needed will never rise above 40 kW - is perhaps an even worse idea. Could someone give me some point about why it's a bad idea so I can relay?

 

[russ_watters]

It depends on the application. Often it is a significant benefit (lower pressure drop, more efficient heat exchange). When you say a "water based central heating system", what exactly do you mean? What is the heat source that heats the water via the plate heat exchanger?

An example where too big is a bad idea is a heating coil in a 100% outside air handling unit. Too big means low fluid velocity, means uneven surface temperature, means you can freeze the water in the coil even when it comes in very hot.

 

[TSN79]

When you say a "water based central heating system", what exactly do you mean?

The hottest side of the exchanger comes from a district heating system (120°C supply). The other side consist of a normal radiator system (supply/return 70-50°C).

 

[russ_watters]

Oh, just water to water: Bigger is better. Just make sure you appropriately size any pumps or control valves .

 

[alphy]

I would advise against using a heat exchanger that is significantly larger than the required heat load for your central heating system. While it may seem like a good idea to have excess capacity, it can actually lead to several issues.

Firstly, using a heat exchanger that is much larger than necessary can result in inefficient heat transfer. This means that your system will use more energy than needed to heat the water, leading to higher energy costs and potentially causing strain on your heating system.

Additionally, a larger heat exchanger may also take up more space and require more materials, which can increase the cost of your system. It may also be more difficult to install and maintain.

Furthermore, a heat exchanger that is too big for the required heat load may not operate at its optimal performance level. This can lead to issues such as increased pressure drop and reduced flow rate, which can negatively impact the overall efficiency of your central heating system.

In summary, it is important to carefully consider the heat load and select a heat exchanger that is appropriately sized for your system. Using a heat exchanger that is too big can lead to inefficiency, increased costs, and potential performance issues.