A couple hundred years ago, we didn’t have artificial refrigeration. In fact, in the early 1800s the Ice Revolution was just beginning, which saw thousands of tons of ice manually cut from lakes and rivers for transport to wanting cities. Can you imagine that today? People and horses cutting the ice from our lakes? An ice-cold drink on a summer’s day involved a lot more work. Today, we are fortunate enough to have refrigeration not just keeping our drinks cool, and meat fresh, but our offices and homes cool and comfortable.
Ice cutting ploughs on Grenadier Pond, 1909. City of Toronto Archives, Fonds 1244, Item 140.
It’s not easy keeping us cool inside during the summer. It’s 30 degrees outside, and you want it say around 23°C. UHN has a policy for offices and clinics to be set between 22.5°C and 24°C in the summer, specialty rooms have their own setpoints. But let’s focus on offices and clinics for now. So, you’re bringing in ventilation air from outside (30°C), which needs to be cooled. Plus you have heat generated by your body, your lights, your computer, and any equipment you have, so that heat needs to be removed. And if you have a window you’re getting solar heat gain from the sun. Windows are especially effective at heating a room; they allow visible light through but block the return infrared radiation, effectively trapping the heat inside your space (which is why they are used for greenhouses).
Let’s start off with what you can do to keep your space cooler and save energy:
- If you have a window, use your blinds appropriately (or get blinds). If you come into work in the morning and your room is hot, close your blinds before you go home each day. If it’s getting hot during the day, close the blinds for a little while.
- Laptops are more efficient and produce less waste heat than desktops, consider switching if you can
- Turn off your computer when you don’t need it
- Make sure you have low energy light bulbs in space (UHN is actively upgrading areas to LEDs)
- Wear lighter clothing in the summer, also lighter colours will reflect the heat
- Drink water frequently, even if you aren’t sweating, your body is losing moisture through respiration and evaporation. Drinking water will allow you do remove heat more effectively.
- If you have an operable window, it’s usually best not to use it when it’s really hot outside (i.e. if it’s hotter than your room setpoint).
These are generally simple things to do whereas providing mechanical cooling is anything but. There are a number of components that go into cooling your space. Let’s start in your room, there are likely diffusers to distribute cool air, there may be heat pumps, or fan coils in the ceiling or by the window. You may have a variable air volume box (VAV) to modulate how much cool air you receive based on your thermostat setting. The VAVs will be connected to a large air handling unit, which serves many rooms and has a cooling coil to cool outdoor air using chilled water (note: cooling coils look much like a car radiators). This chilled water is circulated by pumps and controlled by valves, which get the cold water from the chiller(s) in another mechanical room. Chillers, act much like your refrigerator, but whereas your fridge rejects heat into your room, the chillers at UHN typically reject heat to a cooling tower. A cooling tower pumps water through nozzles to spray onto special heat exchange media, and at the same time pushes or pulls air over the media using large fans.
A simplified chilled water schematic
Here’s an interesting fact which brings us back to the ice harvesting, Toronto General Hospital has 5400 Tons of installed cooling. A ton of cooling is the energy required to melt one ton of ice, so picture 5400 blocks of ice, it’s significant. Across all UHN sites in 2012, a very rough estimate is that we used 25 million kWh to produce chilled water, move it, and thereby cool spaces and equipment. If this estimate is correct, that costs somewhere around $3 million dollars in 2012. But this is our first problem; we don’t actually know how much energy is being used for cooling. We have utility bills that tell us how much energy is going into the building, but after that we don’t know what’s using the energy and thus what could be improved. There’s an old adage, “You can’t manage what you don’t measure”. So how do we get that information? Partially through submetering, which involves installing smaller meters on specific equipment and systems. Submetering is becoming an important and more common tool in operating buildings efficiently.
So overall, what is UHN doing? Well as part of UHNs energy efforts, we are looking at ways to improve:
- the controllability of spaces
- the effective and efficient distribution of cooling
- the efficiency of both creating and moving that cooling energy
- the understanding and breakdown of where our energy is going
Chilled water projects that are actively being pursued include:
- TGH – Optimization of the central chilled water plant and targeted submetering
- TGH – Evaluation and decoupling of process cooling loads
- TWH – Variable speed chilled water flow
- TWH – Real-time commissioning system
- PMH – Controls optimization and recommissioning
- Many more smaller projects and investigations