WHAT IS THE RESNET/ CRESNET HERS INDEX FOR HOMES?
Outside of a mortgage loan, the highest cost of homeownership is energy.
That’s why smart homebuyers ask for a home’s HERS Index Score to determine
its energy efficiency before buying. The HERS Index Score is like a MPG
(miles-per-gallon) sticker for homes. After all, it makes sense to know the
energy performance of a home before making the investment.
DRAIN WATER HEAT RECOVERY AND ITS IMPACT ON THE RESNET HERS INDEX
Drain water heat recovery will increase energy savings, improve home comfort and reduce carbon foot print. It is considered one of the most cost effective ways of reducing the cost of heating water, the second largest energy consumption in a home.
Home Energy Rating System (HERS)
Potential credits: up to 2.1 (70 index home)
DRAIN WATER HEAT RECOVERY SYSTEMS HERS INDEX POINTS RESNET DETAILS
USE THE CALCULATOR TO DETERMINE POINTS OR LATEST HERS SOFTWARE (POST 2016)
Drain Water Heat Recovery (DWHR) – A heat exchanger unit that uses outgoing warm drain water to pre-heat incoming cold freshwater, is rated for efficiency and pressure loss according to CSA B55.1, and complies with CSA B55.2.
Tmains – The temperature of the potable water supply entering the residence.
Add new Normative References to Section 6
CSA B55.1-12, (2012). “Test method for measuring efficiency and pressure loss of drain water heat recovery units.” CSA Group, Mississauga, Ontario, Canada L4W 5N6.
CSA B55.2-12, (2012). “Drain water heat recovery units.” CSA Group, Mississauga, Ontario, Canada L4W 5N6.
NOTE: THERMODRAIN IS CSA 55.1 and CSA 55.2 certified
Table 18.104.22.168.2.11(1) Hot water fixture effectiveness
Plumbing Fixture Description
Standard-flow: showers ≤2.5 gpm and faucets ≤2.2 gpm Feff = 1.00
Low-flow: all showers and faucets ≤2.0 gpm Feff = 0.95
adjFmix = 1 – ((Tset – Tuse)/ (Tset – WHinT))
Tset = 125 oF = water heater set point temperature
Tuse = 105 oF = temperature of mixed water at fixtures
WHinT = water heater inlet temperature
WHinT = Tmains + WHinTadj for DWHR systems and where WHinTadj is calculated in accordance with equation 4.2-14
WHinT = Tmains for all other hot water systems
Tmains = temperature of potable water supply entering the residence calculated in accordance with Section 22.214.171.124.1.4
refFgpd = reference climate-normalized daily fixture water use calculated in accordance with Section 126.96.36.199.1.4
188.8.131.52.2.11.1 Drain Water Heat Recovery (DWHR) Units
If DWHR unit(s) is (are) installed in the Rated Home, the water heater potable water supply temperature adjustment (WHinTadj) shall be calculated in accordance with Equation 4.2-14.
WHinTadj =Ifrac*(DWHRinT-Tmains)*DWHReff*PLC*LocF*FixF Eq. 4.2-14
WHinTadj = adjustment to water heater potable supply inlet temperature (oF)
Ifrac = 0.56 + 0.015*Nbr – 0.0004*Nbr2 = fraction of hot water use impacted by DWHR
DWHRinT = 97 oF
Tmains = calculated in accordance with Section 184.108.40.206.1.4
DWHReff = Drain Water Heat Recovery Unit efficiency as rated and labeled in accordance with CSA 55.1
DWHReff = DWHReff *1.082 if low-flow fixtures are installed in accordance with Table 220.127.116.11.2.11(1)
PLC = 1 - 0.0002*pLength = piping loss coefficient
for standard systems: pLength = pipeL as measured accordance with Section 18.104.22.168.2.11
for recirculation systems: pLength = branchL as measured in accordance with Section 22.214.171.124.2.11
LocF = a performance factor based on the installation location of the DWHR determined from Table 126.96.36.199.2.11(4)
Table 188.8.131.52.2.11(4) Location factors for DWHR placement
Supplies pre-heated water to both the fixture cold water piping and the hot water heater potable supply pipingLocF = 1.000
Supplies pre-heated water to only the hot water heater potable supply piping 0.777
Supplies pre-heated water to only the fixture cold water piping 0.777
FixF = Fixture Factor
FixF = 1.0 if all of the showers in the home are connected to DWHR units
FixF = 0.5 if there are 2 or more showers in the home and only 1 shower is connected to a DWHR unit.