This tech blog was written by our engineer Bill Meyer, of the Cambridge Air Solutions Applications Engineering team.

“Spec” buildings… You gotta love ‘em.

We, at Cambridge are frequently involved with heating “spec” buildings. You know how it goes: a developer puts up the shell, pours the concrete slab, heats the building to a minimum temperature the closes it up with no plans for ventilation. At some point in the future, the developer signs up a tenant and proceeds with the tenant fit-out. That is where our story begins.

The 200,000 sq. ft., 32’ high, uninsulated tilt wall building in Kansas City was erected in 2017 but was not occupied until 2019. In February 2020 our Regional Sales Manager learned from the Property Manager that the tenant was experiencing problems: condensation on the walls and the heaters were not maintaining the desired 55°F space temperature (although the design temperature was 50°F). A Cambridge Applications Engineer was asked to follow up to see if there was anything we could do to help.

Cambridge had participated in a “Building Burp Test” for a similar building in Allentown, PA. The test consisted of running the heating system continuously for 48 hours. The heaters were turned off, the building was ventilated with 1.5 air changes for one hour, and the heaters were turned back on. The indoor moisture level was reduced by 18%, based on datalogger results.

The tenant immediately implemented a similar plan to that outlined in the “Burp Test.” The process helped to dry out the building, but the heaters were still not operating as they should. The next step was to have a Cambridge’s Service Technician visit the job. He was able to get the four Cambridge heaters operating properly by replacing faulty discharge temperature sensors and setting the discharge temperatures to 160°F. The tenant was then able to maintain the desired 55°F space temperature.

Our experience is that providing ventilation significantly reduces moisture problems when buildings are closed up and the concrete slab is curing.
 

THRU WALL UNITS 

Thru wall units are an excellent choice for many warehouse applications. They do not require any floor space. Typically, the units are mounted in shipping/receiving areas to address the cold air gain at the dock doors. 

For manufacturing areas, due to the presence of overhead cranes, thru wall units are frequently not a viable option. The clearance required for an overhead crane at the side wall typically does not allow adequate room to install a thru wall unit. 

The heater may have an external gas train. The gas train should be positioned such that the equivalent distance from the outlet of the gas train to the inlet of the heater does not exceed 4 feet. Usually the best location is to place the gas train perpendicular to the side of the heater, so it can be piped directly into the heater’s gas inlet, as illustrated in the S-Series Technical Manual. 

Servicing the unit is another potential problem if overhead cranes are present. Accessing the unit via a boom lift or scissors lift will entail entering crane space. This usually means that the work cannot take place until the crane(s) is locked out or other measures (such as a blocking crane) are taken. Locking out of cranes may seriously affect production, so it should not be taken lightly. 

Servicing the units utilizing a ladder is frequently not an option due to requirements for safe ladder use. In addition, it is difficult, if not impossible, to access several of the heater’s parts from a ladder. 

If a location for a thru wall unit is found, then consideration should be given to the impact on local work stations. What will the mounting height of the heater be? How will the air be distributed? Double deflection grilles are extremely effective when fine tuning air flow. 

Another potential safety issue is whether plant personnel will be regularly traveling or working beneath the suspended load. Additional safeguards may be needed to secure the heater. 

Installing the unit may require barricading the floor area where the installing crew is working. Plant vehicle & pedestrian control must be considered. Flag men may be required. These aspects will need to be covered in the safe work plan. 

Below are installations of thru wall units that were installed several years ago. As always with retrofit installations, final mounting configuration and placement depends on “what the building gives you” with which to work. 


The Cambridge Air Solutions' Applications Engineering Team is available to discuss custom solutions for your project. Have your local rep engage this team for any specific needs you have!

In new construction, the primary source of moisture entering the building is most likely from the newly poured concrete slab.

The National Ready Mixed Concrete Association (NRMCA) describes the ‘What’ and ‘How’ of concrete slab moisture in their 2004 Concrete in Practice publication CIP 28-Concrete Slab Moisture. Potential sources of concrete slab moisture include:

  • The floor slab is in contact with saturated ground. Moisture moves to the slab surface via capillary action or wicking.
  • Water vapor from damp soil will diffuse and condense on a concrete slab surface that is cooler and at a lower relative humidity due to a vapor pressure gradient.
  • Residual moisture in the slab from the original concrete mixing water will move towards the surface.
  • It may take anywhere from six weeks to one year or longer for a concrete slab to dry out to an acceptable level under normal conditions. Reference: Bruce Suprenant,  Concrete Construction, November, 1997.

The topic is also dealt with in depth by the U.S. Environmental Protection Agency in their publication EPA 402-F-13053. Moisture Control Guidance for Building Design, Construction and Maintenance. December, 2013. Topics include: moisture control in buildings, basics of water behavior, designing for moisture control, constructing to prevent moisture problems, and operating and maintaining moisture-controlled environments.

As manufacturers of HVAC equipment, Cambridge Air Solutions has no input regarding the numerous factors involved in concrete work that affect the moisture in the slab. However, when moisture problems arise, we are often involved in looking for remedies to deal with the moisture. Some of our contractors refer to the procedure “IAQA flush-out, REQEQ2,2r1”, required by LEED and published by the U.S. Green Building Council. https://www.usgbc.org/credits/reqeq22r1-0. This flush-out, as required by LEED, is intended to rid the building of moisture as well as “off gassing” of building materials.

Requirements

Select one of the following two options, to be implemented after construction ends and the building has been completely cleaned. All interior finishes, such as millwork, doors, paint, carpet, acoustic tiles, and movable furnishings (e.g., workstations, partitions), must be installed, and major volatile organic compound (VOC) punch list items must be finished. The options cannot be combined.

Option 1. Flush-out (1 point)

Path 1. Before occupancy

Install new filtration media and perform a building flush-out by supplying a total air volume of 14,000 cubic feet of outdoor air per square foot (4 267 140 liters of outdoor air per square meter) of gross floor area while maintaining an internal temperature of at least 60°F (15°C) and no higher than 80°F (27°C) and relative humidity no higher than 60%. OR

Path 2. During occupancy

If occupancy is desired before the flush-out is completed, the space may be occupied only after delivery of a minimum of 3,500 cubic feet of outdoor air per square foot (1 066 260 liters of outdoor air per square meter) of gross floor area while maintaining an internal temperature of at least 60°F (15°C) and no higher than 80°F (27°C) and relative humidity no higher than 60%. Once the space is occupied, it must be ventilated at a minimum rate of 0.30 cubic foot per minute (cfm) per square foot of outdoor air (1.5 liters per second per square meter of outdoor air) or the design minimum outdoor air rate determined in EQ Prerequisite Minimum Indoor Air Quality Performance, whichever is greater. During each day of the flush-out period, ventilation must begin at least three hours before occupancy and continue during occupancy. These conditions must be maintained until a total of 14,000 cubic feet per square foot of outdoor air (4 267 140 liters of outdoor air per square meter) has been delivered to the space.

Written by Bill Meyer, Cambridge Applications Engineer

For years we have worked with an industrial retrofit contractor. He often installed vertical S-Series heaters in locations where space was at a premium, both indoors and outdoors. Since Cambridge did not provide a stand for vertical units, he had a structural engineer design a four-legged stand made from 2” x 2” square tubing. The legs would be cut to length in the field and a base plate welded to the leg.

This system worked alright but did cause occasional difficulties.

  • Depending upon requirements at the plant where he was installing the heaters, he may have to obtain a burn permit each day, which could result in a delay of an hour or more until the inspector could arrive.
  • He also had to ensure a qualified welder was on the crew, with the appropriate equipment.
  • When possible, he would set up a welding area within the plant so he only had to set up his equipment once. This simplified the burn permit process, but often resulted in double handling the stands when transporting them to and from the location.

The contractor looked to Cambridge to provide a vertical stand that did not require field welding. Cambridge responded with designing the vertical adjustable stand, which provides vertical adjustment while not requiring any field welding.

Due to this success, Cambridge has since added the vertical stand, structural inlet elbow, structural filter section, 3’, 4’ & 5’ vertical duct extensions, adjustable elbow, and 24”, 38” & 50” wall sleeves to our standard product offering.

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Cambridge has been actively supporting our contractor partners with industrial retrofit heating/ventilating projects for over 40 years. Projects include: aluminum rolling mills, automotive/farming/construction/mining equipment manufacturers, tire plants, electrical appliance & motor manufacturing, corrugators, insulation product manufacturing, steel processing plants, bottling & canning plants, warehousing & distribution centers.