“It’s a situation we work very hard to avoid,” admitted Greg Brinkerhoff, director of engineering at the Marriott Kansas City Airport hotel.

According to Brinkerhoff, late arrivers and early risers can push the limits of a hotel’s water heaters and plumbing systems. At his 384-room hotel, adjacent to a busy airport, there’s a steady flow of guests at all hours.

“The highest demand for hot water comes between 5 and 6 a.m. and again between 10 p.m. and midnight,” added Brinkerhoff. It wasn’t uncommon for hotel managers to get several calls a week from guests, displeased about the lack of hot water.

“Unfortunately,” said Brinkerhoff, “The best we could tell them at the time was that hot water ‘was on its way.’”

Hot water woes

At the airport Marriott, hotel managers battled domestic hot water issues for more than two years. As it turns out, a large hydronic valve was used for the original system. The misapplied valve had a 120-second response time and couldn’t actuate quickly to keep up with the changing water pressures present within the hotel.

Because of the valve’s sluggish response time, every time something would go wrong with the pumps, heat exchangers, or storage tanks, the entire domestic hot water (DHW) system would require a time-consuming recalibration. Maintenance was required routinely — a constant source of disruption for the engineering staff.

“More or less, when maintaining the domestic water system, we had to isolate the entire piped network, shutting it down completely,” continued Brinkerhoff. “Whenever the hot water mixing valve opened or modulated, the entire system would flood with cold water.

Instead of being able to run the hot water storage tanks at 150°F, facility engineers had to turn the tanks down to produce storage temperatures of only 125°F. Also, the capacity of hot water storage plummeted.

Enough is enough

Last winter, facility managers and engineers came together and decided to replace the entire hot water system. 

Brinkerhoff was appointed to act as liaison between hotel ownership and the installing contractor. Having worked with him in the past, Brinkerhoff called on Ian Walters, project manager for Kansas City, MO-based Lexington Plumbing, a mechanical contracting firm specializing in commercial and industrial work.

Walters had a solution in mind shortly after speaking with Brinkerhoff about the hotel’s DHW issues.

“Ian and I had this discussion about the hotel’s domestic water system, and that there are just so many dynamic changes with the pumps and water pressures,” said Brinkerhoff. “We knew what the hotel needed a smarter, more responsive valve — especially considering that the guests in all 384 rooms had very different schedules.”

Enter digital mixing

Months earlier, Walters had learned about a digital mixing valve made by Powers, a Watts brand.

The Powers IntelliStation touchscreen control operates a three-way valve through a high-speed actuator to precisely maintain the selected outlet temperature. Temperature and pressure sensors are included at key points within the panel to enable an immediate response to changes in fixture demand and supply water conditions. A built-in pump (optional) provides recirculation of the tempered water loop. This reduces the wait time at point-of-use fixtures and conserves water.

A sanitization mode allows buildings with a thermal eradication protocol in place to control water-borne bacteria to deliver a higher water temperature for a pre-set duration to allow building maintenance staff sufficient time to open all of the fixtures. The unit can be connected to a BAS to provide read access to a range of temperature and pressure measurements and allow adjustment of the outlet temperature setting within a pre-programmed range. BACnet^® IP, BACnet^® MSTP, and Modbus^® protocols are all supported.

“I went with Ian to another Marriott hotel that had similar hot water issues,” Brinkerhoff said. “They’d installed an IntelliStation digital mixing system there, and I was able to see it in operation and speak to facility managers who more than vouched for the system.”

What he learned was that the hotel, which had experienced similar hot water issues, now had a fast-responding, safe, and clean domestic hot water system that delivered hot water on demand. Hearing maintenance managers testify that it only took seconds for hot water to get to taps sold Brinkerhoff.

Hotel guests at the KC Airport Marriott who get hot water fast today will likely never know that their comfort and convenience stems from a digital mixing valve presentation given just a few months earlier by Jamey Shibel, outside sales for manufacturer’s rep firm, Mack McClain & Associates (Olathe, KS).

According to Shibel, sizing and specifying a digital mixing station is relatively simple, with key parameters that include overall gpm, load of the building, pipe sizes, height of the structure, number of rooms and fixtures, and size of utilities such as the laundry and kitchen facilities.

Digital mixing + recirculation

Digital water mixing incorporates a programmable valve or system to quickly process temperature, flow, and pressure data, which is obtained from the hot and cold water inlets, mixed outlet, and sensors on the mixed-water return. High-speed, responsive electronic actuation modulates a simple valve that allows the setpoint to be electronically controlled and maintained.

Digital mixing allows engineers or facility managers to select a desired hot water temperature and to control and monitor the entire water distribution system. For even greater control, these systems can be installed as part of an ASSE-compliant water distribution system, including point-of-use mixing valves at each fixture in the plumbing system. This ensures that hot water storage temperatures can be kept at levels lethal to pathogens and then mixed to safer temperature levels both at points of distribution and use.

Other key advantages to digital mixing include:

• Supports energy conservation through more efficient water temperature management —and in turn reduces energy costs

• Integrates with BAS to support integrated building management

• Supports consistent delivery of hot water on demand wherever and whenever it is needed, in accordance with building codes

Most systems are also field-configurable without the need for a laptop or special software.

Happy guests

Since the installation of digital mixing technology at the hotel, facility managers have yet to receive a hot water complaint. Rather than experiencing the constant headache of boiler room problems and system troubleshooting, Brinkerhoff and his staff merely schedule routine maintenance checks on a six-month cycle.

Varying pressures and temperature fluctuations throughout the hotel’s hot water system no longer pose a threat. While 125°F water is sent to guest rooms in an instant, a second hot water loop now runs 150°F water to the kitchen and laundry areas where higher temperatures are needed for cooking and cleaning. And, water is safely generated and stored at a germ-scorching 175°F.

Four months in with the new digital mixing system, Brinkerhoff says guests are happy.

“And when guests are happy, building owners are happy,” he added. “There are no mixed emotions or opinion on this investment.”