Ammonium sulfate has a well-known order-disorder phase transition at -50 ºC: initially of interest for the ferroelectric behaviour in the low-temperature phase, this has attracted renewed attention recently for its electro- and barocaloric properties. While it is established that this phase transition involves a complex rearrangement of the hydrogen-bond network, its exact mechanism is the subject of continued debate. We propose a total scattering study of the structure in both para- and ferrielectric phases. Using the reverse Monte Carlo method, we will generate atomistic models that reflect both the long-range and the local structure of this material. Our results will isolate the structural changes responsible for ammonium sulfate's electric and caloric behaviour, and contribute towards the development of new materials with these interesting and important properties.