The primary purpose of this document is to provide manufacturers of condensing on-demand water heaters with a route to developing combination systems that provide efficient home space and water heating, and getting the CSA P.9 test results to prove it.
On-demand condensing water heater based combination systems have the potential to be very energy efficient. One of their great advantages is that they can vary the supply water heating temperature in space heating mode to improve overall combination system performance by 10% or more. Engineered packaged systems that control water heating and air handling functions together can condense almost all the time.
This document is intended for managers and design engineers to 1) rapidly understand one approach to developing a high performance combination system 2) help de-risk the development process and use resources most effectively, and 3) set specifications for potential component suppliers. This approach can be customized to deliver a high performance combination system.
The report explains how performance weightings have been set in the standard for systems with different space heating outputs. Space heating part load performance is the key factor in the overall performance rating. For example, with a combo system with a rated 10 kW space heating capacity, space heating part load performance ratings form 74% of the total weighted performance of the combination system.
Recognizing whether a demand is for space or water heating and responding differently is important. Water supply temperatures for space heating must be kept low whenever possible to keep return water temperatures low, and thereby maximize condensing.
The report discusses the components needed, potential controls approaches, and some issues that are anticipated in developing a cost effective and efficient combo using a condensing on demand water heater.
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