SWH System

SS_Main-Nav-SWHSystem

To view the SWH System page, click SWH System on the main window's navigation menu. Note that for the solar water heating system input pages to be available, the technology option in the Technology and Market window must be Solar Water Heating.
ico-minus-16x16Overview

The SWH system page displays characteristics of the solar water heating system and allows you to define the hourly hot water draw of the system.

Keep the following in mind as you use Solar Advisor's solar water heating model:

•Solar Advisor calculates the water mains inlet temperature is based on the correlation to local air temperature used in the Building America Benchmark.
•The flow rate is assumed constant over each hour, using values from the hourly hot water draw profile that you specify. Solar Advisor calculates the flow rate in kg/hr as the draw volume in kg for a given hour divided by one hour.
•Collectors are assumed to be flat plate collectors plumbed in parallel, with uniform flow through each collector at the tested flow rate.
•Collectors are characterized by the linear form of the collector efficiency and IAM (incident angle modifier) equations, with parameters available from test data (e.g., www.solar-rating.org), or by external calculation for untested collectors.
•The collector loop is assumed to be charged with glycol having Cp = 3.4 kJ/kG-ºC, with no correction to the collector parameters.
•The heat exchanger is external to the solar tank, has no thermal losses, and is assumed to have the constant effectiveness that you specify on the SWH system page.
•A standard differential controller controls the solar and storage tank loop pumps. Pump power is 40W for both solar loop and storage loop pumps, and pump energy is assumed totally lost.
•Tanks are modeled with a finite difference approach. The solar and auxiliary storage tanks each are modeled with 3 nodes, accommodating modest stratification. The solar tank loss coefficient is the Tank U Value specified on the SWH system page. The auxiliary tank loss coefficient is calculated from the water heater energy factor specified on the SWH system page. The model assumes  a single electric element located at the bottom node of the auxiliary tank, witha  maximum capacity of 4.5 kW. A tempering valve is placed at the outlet of the auxiliary tank, with setpoint equal to the water heater set temperature on the SWH System page.
ico-minus-16x16Input Variable Reference

Orientation

Collector Tilt (degrees)

The array's tilt angle in degrees from horizontal, where zero degrees is horizontal, and 90 degrees is vertical. As a rule of thumb, system designers often use the location's latitude (shown on the Climate page) as the optimal array tilt angle. The actual tilt angle will vary based on project requirements.

Collector Azimuth (degrees)

The array's east-west orientation in degrees. An azimuth value of zero is facing south in the northern hemisphere. Positive 90 degrees is facing due west and negative 90 degrees is facing due east. As a rule of thumb, system designers often use an array azimuth of zero, or facing the equator.

Hourly Hot Water Draw

You must specify a set of 8,760 hourly values representing the hot water system's heating load. You can either import values from a text file, paste values from a spreadsheet or other file using your computer's clipboard, or type a set of 24-hour load profiles for each of the twelve months of the year, with the option of specifying separate profiles for weekdays and weekends.

See Specifying the Hot Water Draw for details.

Water Draw (kg/hr)

The mass of hot water drawn over an hour. Click Edit to specify the hot water draw.

The mean, min, and max values displayed in the small box next to the Edit button display the mean, minimum and maximum values in the current data set.

System Parameters

 

Collector Area (m2)

Total collector area, consistent with the area convention used in the collector efficiency equation (e.g., use gross area for all SRCC data)

FRta

Optical gain a in Hottel-Whillier-Bliss (HWB) equation hcoll = a – b x dT

FRUL (W/m2-°C)

Thermal loss coefficient b in the Hottel-Whillier-Bliss (HWB) equation hcoll = a – b x dT

Incident Angle Modifier Coeff

The constant b0 in the equation IAM = 1 – b0 x (1/cos(q) – 1)

Heat Exchanger Efficiency

Heat exchanger effectiveness, where the effectiveness e, is defined as e ≡ (Tcold-out – Tcold-in) / (Thot-in - Tcold-in)

Tank Height/Diameter Ratio

Defines the solar storage tank geometry, and by extension its geometry.

Storage Volume (m3)

The actual volume of the solar storage tank. Note that the actual volume may be different from the rated volume.

Solar Storage tank U value (kJ/h-m2-ºC)

the solar storage tank loss coefficient. Note that 1 kJ/h-m2-C = 3.6 W/m2-C).

Water Heater Energy Factor

The electric auxiliary water heater's energy factor, from the U.S. Department of Energy standard test for water heaters, where the energy factor, EF, is defined as EF ≡ QToLoad / QAuxiliary

Water Heater Volume (m3)

The actual volume of the electric auxiliary tank. Note that the actual volume may be different from the rated volume.

Water Heater Set Temp (ºC)

The temperature setpoint for the heating element of the electric water heater.

Calculated System Size

Nameplate Capacity

The system's nominal capacity in thermal kilowatts, used to in capacity based cost and financing calculations, and to calculate the system capacity factor reported in results. The capacity, P is given by P = AColl x FRta - FRUL x 30/1000, where AColl is the collector area.
ico-minus-16x16Specifying the Hot Water Draw

The hot water draw represents the solar water heating system's hourly thermal load over the period of one year.

A load data file is a text file with 8,761 rows: The first row is a text header that Solar Advisor ignores, and the remaining 8,760 rows must contain average hourly electric demand data in kilowatts. The first data element represents the hour beginning at midnight and ending at 1 a.m. on January 1.

To import load data from a properly formatted text file:

1.On the SWH System page, click Edit.
2.In the Edit Hourly Data window, click Import.
3.Navigate to the folder containing the load data file and open the file.

Solar Advisor displays the data in the data table. Use the scroll bars to see all of the data.

4.Click OK to return to the SWH System page.

To import load data from a spreadsheet or other file:

1.On the SWH System page, click Edit.
2.Open the spreadsheet containing the load data. The data must be in a single column of 8,760 rows, and expressed in kg.
3.In the spreadsheet, select the load data and copy it.
4.In the Edit Hourly Data window, click Paste.
5.You can also copy data from the Edit Hourly Data window by clicking Copy, or export the data to a text file by clicking Save.

If you do not have a complete 8,760 set of load data, you can use a set of daily load profiles for each month, and use Solar Advisor to create a set of 8,760 values.

To create a load data set using daily load profiles:

1.On the SWH System page, click Edit.
2.In the Edit Hourly Data window, check Use monthly grid to generate 8760 data.
3.For each month of the year, define a daily load profile by typing a kg hot water draw value for each of the 24 hours of the day. The first column represents the first hour of the day, beginning at midnight and ending at 1:00 a.m.

If you want to specify separate load profiles for weekdays and weekends, click Weekend Values to define profiles that apply to two days each week. Solar Advisor arbitrarily assumes that the first day in the data set is a Monday, and that weekends fall on Saturday and Sunday.

If you do not specify separate weekend profiles, Solar Advisor applies the weekday profile to all days of the week.

4.When you have specified all of the daily load profiles, click To 8760 to transfer the data to the User Specified data table. You must complete this step for Solar Advisor to use the profile data in simulations.

When you define a load with daily load profiles, Solar Advisor assumes that all days in a given month have identical load profiles.

5.If you want to export the 8,760 data to a text file, click Save. You can also copy the data to a spreadsheet or other file by clicking Copy, and then pasting the data in to the file.