Skylights Vertical vs. Splayed

SkylightsVertical vs. SplayedVertical vs. Splayed

By: Lisa Bornemann By: Lisa Bornemann

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Brad KoehlerBrad Koehler

GoalsGoalsFor our final project, we studied the skylight system found in the University Support Building, located For our final project, we studied the skylight system found in the University Support Building, located across Park Avenue. There are large skylights through the main corridor of the support building. We across Park Avenue. There are large skylights through the main corridor of the support building. We chose to study the changes in illuminance levels while varying the parameters of the skylight. chose to study the changes in illuminance levels while varying the parameters of the skylight.

In this presentation, we took actual measurements with an illuminance meter and we ran Radiance In this presentation, we took actual measurements with an illuminance meter and we ran Radiance for the same situation. These numbers turned out to be quite different in magnitude, but the for the same situation. These numbers turned out to be quite different in magnitude, but the patterns of higher or lower illuminance values were the same. These values may differ because the patterns of higher or lower illuminance values were the same. These values may differ because the dimensions of the real skylight well, the height of the glass pyramid, and the width of the mullions dimensions of the real skylight well, the height of the glass pyramid, and the width of the mullions were eye balled. Also, while we were taking the measurements, the sky conditions were relatively were eye balled. Also, while we were taking the measurements, the sky conditions were relatively clear, but there were clouds in the sky that would block the sun at times. We waited patiently to clear, but there were clouds in the sky that would block the sun at times. We waited patiently to take the measurements when the sun was not being shaded by clouds and the area of the sky above take the measurements when the sun was not being shaded by clouds and the area of the sky above the skylight was relatively clear. Still, with some puffy clouds in the sky, they may have affected the the skylight was relatively clear. Still, with some puffy clouds in the sky, they may have affected the results as compared to the description of what clear sky conditions is on Radiance which is the results as compared to the description of what clear sky conditions is on Radiance which is the condition we used to run our tests.condition we used to run our tests.

Throughout the presentation we have shown our different modeled situations and the illuminance Throughout the presentation we have shown our different modeled situations and the illuminance measurements obtained through running Radiance. We will compare these measurements and measurements obtained through running Radiance. We will compare these measurements and explain how the different parameters change the output data. The actual skylight has a 10 foot well explain how the different parameters change the output data. The actual skylight has a 10 foot well with a 9 ft. by 9ft. opening. The glass is in a 3 ft. high pyramid shape with 4 in. mullions. We have with a 9 ft. by 9ft. opening. The glass is in a 3 ft. high pyramid shape with 4 in. mullions. We have chosen to discuss four modified situations: a 5 foot well, no well, a 5 foot splayed and 5 foot vertical chosen to discuss four modified situations: a 5 foot well, no well, a 5 foot splayed and 5 foot vertical well, and a 5 foot splayed with no vertical well.well, and a 5 foot splayed with no vertical well.

For a corridor, only 5 footcandles is required according to the IES handbook. The average illuminance For a corridor, only 5 footcandles is required according to the IES handbook. The average illuminance with the current skylight is about 250 footcandles. So obviously the requirement is met. In this with the current skylight is about 250 footcandles. So obviously the requirement is met. In this presentation, we are not going to determine which skylight is the best, but we are going to explain presentation, we are not going to determine which skylight is the best, but we are going to explain how the illuminance levels change with the different situations. This information can then be used how the illuminance levels change with the different situations. This information can then be used to determine which skylight will be the best design for particular situations requiring different to determine which skylight will be the best design for particular situations requiring different illuminance levels.illuminance levels.

Information UsedInformation Used

The transmittance of the glazing was calculated by taking the illuminance outside and the luminance inside aimed at the skylight glass.

Lemitted= 805 cd/m2

Eincident = 4900 luxTransmittance = Π*Lemitted / Eincident = 0.52

*Note: Transmittance used in Radiance is 0.534

Sky conditions for all situations were considered clear.Sky conditions for all situations were considered clear. The date the measurements were made and calculations were ran for April 18The date the measurements were made and calculations were ran for April 18 thth.. All actual measurements were made between 2pm and 3pm, so in Radiance, the time used was 2:30 All actual measurements were made between 2pm and 3pm, so in Radiance, the time used was 2:30

pm.pm. All illuminance measurements shown throughout the presentation are in footcandles.All illuminance measurements shown throughout the presentation are in footcandles. Throughout the presentation, four corner points will be discussed. Corner 1 through 4 in the counter Throughout the presentation, four corner points will be discussed. Corner 1 through 4 in the counter

clockwise direction. The color key below will help make them easier to reference:clockwise direction. The color key below will help make them easier to reference:corner 1corner 1corner 2corner 2corner 3corner 3corner 4corner 4

Original Design ~ 10 ft. WellOriginal Design ~ 10 ft. Well

Actual illuminance levels obtained by Actual illuminance levels obtained by taking measurements with an taking measurements with an illuminance meter at the site:illuminance meter at the site:

230 243 262 274 283 293 279 254 239

236 245 288 284 302 298 291 289 274

260 278 289 303 313 302 305 295 275

259 279 284 293 306 306 300 289 274

244 255 269 264 295 298 290 279 264

234 245 258 264 269 274 270 263 248

229 236 247 253 258 265 252 243 235

221 229 240 248 251 257 243 238 229

216 222 233 241 243 249 238 231 220

489 512 455 435 455 497 502 527 516

532 461 467 444 473 468 568 548 536

363 430 449 435 485 517 538 464 451

383 443 452 420 427 456 453 447 439

407 415 424 431 453 486 479 472 464

415 401 412 440 496 489 456 449 401

393 400 359 357 354 492 441 429 416

342 321 366 382 402 396 434 420 373

344 322 374 399 395 437 395 385 363

5 ft. Well5 ft. Well

406 451 566 567 536 459 442 396 398

433 392 504 442 434 451 422 388 399

464 419 471 462 452 470 466 430 386

448 453 443 482 487 476 442 392 375

475 465 511 502 491 480 463 410 392

567 548 533 592 544 500 482 463 475

605 592 633 613 539 494 532 513 480

631 671 651 632 554 495 484 457 429

691 690 667 645 566 550 568 535 497

In this model, the illuminance striking the floor was higher than the illuminance on the floor of the 10 ft. well design. We feel that because this well is smaller than the previous, there are fewer bounces of reflected light. The result is a higher illuminance level across the floor because less light is absorbed by the well walls.

Also, you will notice that corner 2 has the highest illuminance of all of the corners while in the 10ft. well, the diagonal corner (corner 4) has the highest illuminance. We feel this occurs because in the shorter well, more light directly hits the floor opposite the sun. Corner 2 is getting directly hit by the sun’s rays.

No WellNo Well

400 402 404 394 382 372 362 340 319

457 454 449 442 427 419 399 376 350

511 510 501 489 470 463 438 412 378

580 571 554 537 524 499 476 444 408

644 608 595 581 567 538 505 475 435

691 664 652 645 620 583 549 508 459

754 747 716 689 663 629 580 525 476

817 805 758 733 711 671 598 548 498

890 823 797 786 741 658 619 570 513

In this model, the illuminance striking the floor was higher than the illuminance on the floor of the 5 ft. well design. We feel again that because there is no well, there is no reflected light. The result is a higher illuminance level across the floor because no light is absorbed by the well walls.

The pattern formed on the illuminance grid is the same as the 5ft with the highest illuminance in corner 2.

Splayed w/ 5 ft. WellSplayed w/ 5 ft. Well

445 450 458 455 447 423 407 377 366

474 481 482 473 469 446 403 392 381

508 511 502 499 492 465 447 462 442

541 532 529 514 515 502 496 476 459

565 559 547 534 530 529 509 489 474

584 578 566 552 572 542 523 502 484

626 606 659 629 590 561 539 516 494

685 679 677 647 617 584 550 521 497

729 725 695 665 637 586 557 528 503

In this model, the illuminance striking the floor was higher than the illuminance on the floor of both the 5ft and 10ft wells. The splayed parts of the well will reflect light downward with less bounces. Also, a splayed well yields a larger source of light. We feel these are both reasons that the illuminance is higher.

The pattern formed on the illuminance grid is the same as the 5ft and no well with the highest illuminance in corner 2.

Splayed w/out WellSplayed w/out Well

In this model, the illuminance striking the floor was higher than the illuminance on the floor of the splayed with a 5ft well. Less bounces occur because there is no vertical well. Also, a splayed well yields a larger source of light. We feel these are both reasons that the illuminance is higher.

The pattern formed on the illuminance grid is the same as that of the splayed with a 5 ft well with the highest illuminance in corner 2.

486 487 492 488 479 501 478 453 426

532 524 527 553 532 524 509 483 458

583 601 617 597 576 557 542 514 473

679 663 653 643 621 595 559 530 496

739 723 707 692 656 617 585 559 520

804 770 753 740 702 662 609 576 542

880 847 824 789 750 737 639 603 559

978 903 848 799 834 777 694 624 579

1092 973 918 934 879 820 691 645 598

Radiance RenderingRadiance RenderingVertical WellVertical Well

Radiance RenderingRadiance RenderingSplayed w/ 5ft WellSplayed w/ 5ft Well

ConclusionConclusion

A shorter vertical well will yield a higher illuminance level on the floor A shorter vertical well will yield a higher illuminance level on the floor due to less light being absorbed by the well walls.due to less light being absorbed by the well walls.

A splayed well will yield higher illuminance levels than a vertical well A splayed well will yield higher illuminance levels than a vertical well of similar proportional.of similar proportional.

A splayed well becomes a larger light source and will therefore A splayed well becomes a larger light source and will therefore spread more light over a larger area, thus increasing the illuminance spread more light over a larger area, thus increasing the illuminance directly below the well.directly below the well.