Hydronic Air Conditioning +Heating System with Rainwater Thermal Storage


Air conditioning is the primary component of power demand and energy consumption in Texas. To alleviate afternoon electricity grid congestion, and avoid higher-priced power, NexusHaus will incorporate an Integrated Thermal Energy and Rainwater Storage (ITHERST) system to shift air conditioning load off-peak to the early morning hours. Thermal storage technology has traditionally only been employed on the large commercial and industrial scale; however, NexusHaus will demonstrate the concept’s effectiveness on a residential scale.

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The ITHERST system operates the thermal storage tank as an auxiliary rainwater collection and storage volume which increases the effective capacity of the rainwater collection system and makes use of an otherwise un-utilized thermal mass. Figures 1-3 contain a schematic representation of the main components and operation of the ITHERST system. Analyses performed by the NexusHaus team suggest that the ITHERST system could reduce the on-peak cooling-related electricity load (compared to the same system without thermal storage) by 75-80%, with a corresponding increase in electricity consumption of approximately 5-10%, when operating in Austin, Texas. The modest increase in energy consumption occurs during low-demand off-peak hours, when prices are lowest and West Texas wind is typically blowing strongest. (As part of their electricity generation, Austin Energy – the only electric utility available to Austinites – utilizes turbines located in the western half of the state where winds are strongest.)



This system, coupled with the solar PV system, provides electricity to the grid on-peak while simultaneously reducing the house load, as shown in Figure 1. The goal is not just to minimize air conditioning load on the grid, but to also provide as much excess energy as possible to support the surrounding neighborhood when power is needed most. Additionally, this approach benefits other grid-connected stakeholders, from customer to utility, and could therefore be a source of savings and/or revenue generation. The thermal storage system will save the home occupant on their utility bills by making use of real-time or time-of-use pricing.


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