[DESIGN] - Dehumidification

nchareunsouk commented 3 years ago

Completion is tracked in the linked PR.

Design Scope

Design a system to decrease the air water vapour content of the internal environment.

Purpose

The purpose of the dehumidification system is to control the "extraction" of water vapour from the internal environment while a) not introducing pathogens and/or other aerosols to the outside environment, b) minimizing waste water (aka maximizing recapture), and c) maximizing the precision of the internal environment.

Note on scope: We have eliminated a number of methods for dehumidification:

Condensation (i.e. a cold surface causes vapour to collect for recapture) - introduces "cross-talk" with thermoregulation
...

Thus we have scoped in to chemical extraction via "desiccants".

Function

Inputs:

Power
Dehumidification control systems (fan speed and shutter open/close)
Dry desiccant

Outputs:

Saturated desiccant
Saturation indicator signal (color sensor)

It interfaces with/depends on the following systems:

Power delivery
Operator notification (for desiccant replacement)

System operation assumes:

An external "oven" capable of drying saturated desiccant, with either a) ability to recapture water vapour (preferred), or b) capacity to handle water vapour

Method

Setup:

Dehumidification control signals are hooked up
Dry desiccant is added to cartridge, which is inserted

Process:

Humidity sensor sends data to control module
Dehumidification control signal activates fans and opens shutters
Humid air passes over the desiccant, and dry air exits the unit
Desiccant becomes saturated, and indicates this
Indication is sensed by computer, which notifies the user
Cartridge is removed by the user, and swapped for a dry one. Process continues
Saturated cartridge is recharged

Shutdown:

Control signals are disconnected
Final recharging of cartridge
Desiccant is removed from cartridge

Features

Each feature should be added to relevant BoMs and CADs where applicable. Design decisions should be well-supported using relevant research and calculations, and should be documented in the Solution Overview. If a feature is complex enough, create a new issue for it using this template, and tag it here.

[ ] Humidity Sensors (integrated with Temperature Sensors in #122)
[ ] Dehumidification Unit: One input port and one output port. Comprised of:
- [ ] Fans: Draws moist air through input port and dried air through output port.
- [ ] Filter: HEPA filters are located at ports of dehumidification chamber. Eliminates risk of any airborne pathogens being transferred onto silica beads.
- [ ] Airtight Shutters - Isolates dehumidification chamber when not in use. Prevents unintended dehumidification. Located at input and output ports. Controlled by a servo.
- [ ] Desiccant Cartridge: Oven-safe. Easily removable for swapping and "recharging".
- [ ] Silica Beads: Cheap, efficient, non-toxic desiccant. Changes color when saturated. Can be reused indefinitely when water is evaporated.

Requirements and Validation

What does this design need to accomplish? How do we know it has accomplished this?

List any applicable metrics with criteria/constraints, applicable to purpose, function, method, and each feature, as well as how to test them.

Desiccant removes moisture from air
Desiccant indicates saturation as expected, which is sensed by computer
Shutters operate as intended, and no dehumidification occurs when closed
Maximum dehumidification rate exceeds total plant transpiration rate

Verification

Each test should be performed and documented, and the testing documentation attached to the PR. The testing suite should address the full scope of the function (i.e. ensure inputs are met and outputs work), method (all steps execute correctly), and features (each feature performs as expected) with respect to the purpose and requirements.

How does this design achieve its method effectively, safely, and reliably? How do we test this?

Specific testing procedure:

Test shutter and fan operation, shutter air-tightness (zero unintended dehumidification), and air throughput (maximum and precision)
Test cartridge replacement efficacy
Test aerosol filtration
Test dehumidification (maximum rate, rate control precision)

Additional context

Add any other context about the design scope or additional deliverables here.