Waste Water Heat Recovery for Showers
Is your Passivhaus still leaking energy?
Passive House (or Passivhaus) is one of the Worlds’ most rigorous design standards for both residential and commercial buildings. Enhanced airtightness and exceptional levels of fabric insulation underpin the Passivhaus design ethos and prevent heat energy from leaving the building envelope, which can ultimately bring the space heating requirements in Passivhaus dwellings down to around 90% of that of typical building stock [1], and in many cases down to zero.However, there may be heat energy losses from Passivhaus or other modern highly insulated homes designs that are not being considered, yet could form a significant part of the energy budget.“Just because your house is super-insulated, doesn’t mean you necessarily bathe more or take shorter showers!”The energy requirements for domestic hot water (DHW) for Passivhaus dwellings are likely to be roughly the same as they are in equivalent regular houses [2 & 3] (Figure 1). Therefore, the hot water generation in a Passive House (and many other highly insulated modern homes) can form the largest part of the household energy budget, with the DHW energy requirement commonly being 3-4 times larger than the energy required for space heating. (Figure 2).
Data gathered by the Energy Saving Trust from over 86,000 households can be calculated to show that in the average UK home showering accounts for 50% of the generated hot water cost (4). However, around 85-90% of this heat energy goes straight down the drain(5) . That’s around 42% of the total dwelling DHW budget!In a Passive House with a similar energy usage profile to that in Figure 2, DHW generation accounts for 48.9% of the overall energy budget, and assuming the showering habits of those in Passive houses do not differ from the average home, then a staggering 20.80% of the energy used in a Passivhaus could be pouring out of the building envelope via the shower drain.
Air tightness 1: Water tightness 0!
WWHRS is designed specifically to capture this wasted heat energy and recycle it back into the building DHW system, and the good news is, it can be designed into Passivhaus dwellings as cheaply and efficiently as it can for any other newbuild dwelling.The Recoup Pipe+ HE is up to 67% efficient and can, therefore, recover a significant proportion of this drain water heat energy that is otherwise be wasted and flushed away. What’s more a number of the Recoup WWHRS products such as the Pipe+ HE and Drain+ are listed on the Passivhaus Institute: Certified Component Database, and so can be used directly to contribute towards Passivhaus certification or PHPP calculations, and more importantly, reduce energy leaking from the dwelling via the waste-water pipes.
Passive house designers and end-users are more than comfortable with the concept of MVHR being used to exchanger heat energy from stale air and recycled to inbound fresh air, despite the potential design and maintenance headaches that can arise from these systems. However, WWHRS is a much simpler solution that has no moving or mechanical parts; requires no planned maintenance; and no end-user interaction. It’s a fit and forget technology that that simply offers on-demand energy savings with every shower.Don’t you think it’s time that Passivhaus designers and their clients, started to seriously look at WWHRS as a primary method of reducing DHW energy escaping from the building envelope?Please feel free to comment below, or contact us directly to find out more:[1]http://passivehouse.com/02_informations/01_whatisapassivehouse/01_whatisapassivehouse.htm[2]The importance of hot water system design in the Passivhaus’. Nick Grant and Alan Clarke, 2010[3] http://www.ech2o.co.uk/time-for-passive-house-designers-to-address-hot-water-demand-2[4] Energy Saving Trust: At Home with Water, 2013.[5] BRE – Standard Assessment Process calculation for instantaneous WWHRS
