Energy Advisor – RESNET & CRESNET

RESNET & CREASNET

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.

RESNET DWHR Tool

ANSI RESNET


DRAIN WATER HEAT RECOVERY SYSTEMS HERS INDEX POINTS RESNET DETAILS

WHAT IS THE RESNET/ CRESNET HERS INDEX FOR HOMES?

ANSI RESNET

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 4.2.2.5.2.11(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))

Where

Tset = 125 oF = water heater set point temperature

Tuse = 105 oF = temperature of mixed water at fixtures

WHinT = water heater inlet temperature

Where

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 4.2.2.5.1.4

refFgpd = reference climate-normalized daily fixture water use calculated in accordance with Section 4.2.2.5.1.4

4.2.2.5.2.11.1 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

Where

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 4.2.2.5.1.4

DWHReff = Drain Water Heat Recovery Unit efficiency as rated and labeled in accordance with CSA 55.1

Where

DWHReff = DWHReff *1.082 if low-flow fixtures are installed in accordance with Table 4.2.2.5.2.11(1)

PLC = 1 – 0.0002*pLength = piping loss coefficient

Where

for standard systems: pLength = pipeL as measured accordance with Section 4.1.1.5.2.11

for recirculation systems: pLength = branchL as measured in accordance with Section 4.2.2.5.2.11

LocF = a performance factor based on the installation location of the DWHR determined from Table 4.2.2.5.2.11(4)

Table 4.2.2.5.2.11(4) Location factors for DWHR placement

DRHR Placement

LocF

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

Where

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.