Humidity change rate control in intermittently heated historic buildings

Magnus Wessberg,Tor Broström,Tomáš Vyhlídal

doi:10.1051/e3sconf/202017215004

Magnus Wessberg, Tor Broström + Show 1 more

Open Access

https://doi.org/10.1051/e3sconf/202017215004

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Abstract

Many massive historic buildings such as stone churches are intermittently heated. The predominant heating strategy is to heat the building with as high heating power as possible to achieve a fast and energy efficient heat-up process. However, the fast change rate of temperature induces a high change rate of relative humidity, which can be dangerous for interiors and objects in churches. It has been suggested that the change rate of relative humidity should be limited with respect to conservation. Desorption from the walls has a significant effect on the change rate of relative humidity. Typically, the absolute humidity can increase by 50% when the church is heated. Based on a hygrothermal model that allows for a prediction of both temperature and absolute humidity as function of time, this paper presents a model-based feed-forward control algorithm that calculates the maximum hourly heating power increase allowed for limit the change rate in relative humidity to a pre-defined value. The control algorithm is validated using simulations.

Highlights

Many historic building have been heated intermittently with open fireplaces or stoves [1]
Based on a hygrothermal model that allows for a prediction of both temperature and absolute humidity as function of time, this paper presents a model-based feed-forward control algorithm that calculates the maximum hourly heating power increase allowed for limit the change rate in relative humidity to a pre-defined value
The objective of the present paper is to present a simplified hygrothermal model that allows for control of relative humidity (RH) with respect to conservation during intermittent heating

Summary

Introduction

Many historic building have been heated intermittently with open fireplaces or stoves [1]. Even with more modern heating sources, intermittent heating is still common in historic buildings as it provides a reasonable comfort in combination with relatively low energy use [2]. The building is heated rapidly before use and in between, the building is kept cold or with background heating. The thermal models for intermittent heating were established already in the 19th century [3]. More recent research have shown how these models can be practically used in order to predict heat up time and to determine the proper heating power when installing a new heating system [4, 5]. For a given temperature increase, with respect to thermal comfort, we must consider how much the RH would change and how quickly it changes. The relation between T and RH is not trivial as moisture is added to the air through desorption from wall as result of heating

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