Engineers who pull out the 2015 ASHRAE Handbook HVAC Applications or 2016 HVAC System and Equipment Handbook will not find the topic of temporary HVAC systems. And yet, these applications probably occur on half of the major construction projects each year. If the engineer Googles “designing a temporary HVAC building system,” the internet will bring up numerous pages listing companies that rent, install, operate, maintain, and remove temporary heating equipment/systems as well as ventilation equipment and cooling equipment/systems.



As a rule, temporary HVAC is left up to the imagination of the contractor, and it is usually based on carrying a bare minimum cost to the project. I have even experienced HVAC subcontractors carrying a “plug number” for temporary heating on jobs, hoping the number won’t eliminate them from being awarded the job. After all, without a detailed scope of work within the contract documents, how do you carry the right price in a competitive design-bid-build project delivery environment? Construction managers and integrated project delivery builders have more flexibility when it comes to carrying a “temporary heat allowance.” They can develop a budget and work with the building owner to come to an agreement that sounds feasible but not based on any specific design criteria.

Stepping back and cataloging temporary HVAC, here are the most common applications:

  1. Heating. (a) During a new construction or renovation project in the heating season. (b) During an infrastructure replacement (i.e., boiler replacement). (c) During a period when an existing boiler plant has failed.

  2. Ventilation. (a) During a new construction or renovation project to maintain negative pressure to the dirty construction space. (b) To provide makeup air to a smoke filled area during construction (i.e., welding within a confined area).

  3. Air conditioning. (a) During a new construction or renovation project in the air conditioning season. (b) During an infrastructure replacement (i.e., chiller replacement). (c) During a period when an existing chiller plant has failed.


One can dissect these scenarios further, but these are the usual temporary system and/or temporary equipment opportunities. Seldom in my design and construction experience has an owner requested the design team to engineer a temporary HVAC solution based on upcoming weather conditions, existing primary equipment failure, or design criteria.

That said, how does one go about providing a cost effective — and equally important — environmentally friendly solution to address temporary needs? Sure, one can simply buy a few direct, gas-fired heaters that blast the air down a corridor on a construction site. As the saying goes, “bigger is better,” and the cost will get passed on to the owner in one way or another. Or, the design team, working with the contractor, could allow the new HVAC system to provide temporary HVAC during the construction phase, but that is a topic for another article.



There are several scenarios that experienced building owners and/or design engineers may face and will ask the question(s) as follows:

  • Needing temporary HVAC, will my project contribute to or against the environment?

  • Can the project collect LEED credit for its temporary HVAC equipment/system?

  • Based on limited number of hours requiring mechanical cooling during the cooling season, can the building be engineered and built to accommodate an air conditioning system but without purchasing the primary cooling equipment?

  • Can a building program include furnishing and installing an air conditioning system but not authorize purchasing the primary cooling equipment?

  • What if a building owner, company, or community strategically chooses to not purchase the primary HVAC equipment as part of their building program budget?

  • What if a building owner, company, or community strategically chooses to not purchase the primary HVAC equipment to avoid the annual O&M and service cost?

  • With existing heating or cooling equipment that struggles to satisfy peak season heating and/or cooling demand, can infrastructure operation strategy address these peak demands without adding more heating or cooling equipment?

  • With existing heating or cooling equipment reaching its end-of-useful service life, but without knowing when new equipment funds can be authorized, can infrastructure operation strategy address peak demands in the interim and until funds are committed to adding new infrastructure HVAC equipment?


There can be several value-added reasons to not invest in primary HVAC equipment, beginning with project first cost. A risk assessment decision to not purchase the primary equipment would need to include a contract with a local temporary HVAC firm capable of providing the equipment on demand within a specific response time. The design team would need to incorporate into their design intent a delivering plan, equipment setup, operation, maintenance, and removal plan for the primary equipment (Table 1).

This No Primary Equipment Purchase Plan would require a long-term, annual owner-contractor temporary HVAC agreement. Part of this engineered solution would be the comparison between the owner’s first cost to furnish, install, operate, and maintain the primary equipment versus the long-range rental cost and its associated O&M cost. Part of this evaluation would also take into account annual costs associated with having qualified in-house operators and/or service contractor costs, versus costs to outsource the equipment and the same O&M to a temporary HVAC contractor.

Why would any owner consider this as a viable business option? Here are at least six reasons to have a temporary HVAC action plan:

  1. No HVAC equipment first cost in the building program’s construction budget.

  2. No equipment room space requirement in the building program’s construction budget.

  3. No equipment room first cost (general construction, mechanical, electrical, plumbing, or fire protection associated with the primary equipment) in the building program’s construction budget.

  4. No in-house O&M labor cost (e.g., specialized/licensed trade labor) in the annual operating budget.

  5. No in-house O&M inventory cost (e.g., parts and material) in the annual operating budget.

  6. No end-of-useful service life replacement cost in the deferred maintenance budget.



Over the years, I have been involved with a select few progressive facility managers who considered temporary HVAC equipment/systems as part of their building’s value engineered solutions to building infrastructure when faced with first cost and/or annual O&M costs. At one hospital in the northeast, the hospital had grown in square footage, but expanding the central chiller plant never got into the construction budget. The facility expanded in size, but no additional air conditioning equipment was added to serve the new space. Right or wrong, that is what it was and so the very knowledgeable facility manager asked me what were his options to accommodate peak air conditioning demand, as well as what to do if one of his antiquated chillers failed. From this discussion, we came up with a temporary air conditioning capacity plan.

The easy answer was to add a new chiller plant extension, but at $2,000 to $3,000 per ton for a new chiller with associated pumps, piping, etc., tied into the central chiller plant, this solution was not a financial option. In addition, there was no space available to expand the existing chiller plant or add a separate stand-alone second cooling plant structure. Plan B was to consider aligning the hospital with a local chiller rental company that guaranteed delivery and start-up within 24 hours if the hospital would sign an annual contract and also furnish and install the necessary valve and capped pipe system termination points just outside the building in an area where the rental company could conveniently leave their two flatbed trucks (chiller and generator).

Elsewhere, a local school department in the south included within their new middle school building program an emergency action plan providing a temporary shelter for displaced residents due to extreme weather conditions. Should a disaster occur, this new school’s 2-pipe heating system would be zoned to provide chilled water to the central AHUs servicing the field house. Delivered on a flatbed truck, a temporary chiller could provide temporary cooling to the shelter/field house when a disaster occurred during the summer months. It could also occur should a special event happen in the field house during the air conditioning season.

A major sports team had the vision to incorporate into their new training field house the ability to truck in mechanical cooling to serve their new central AHUs. During the offseason, the field house would become a revenue source as an entertainment center, providing air conditioning to their practice field house for annual events (i.e., camper and boat shows). The decision was to invest in the temporary air conditioning units to deliver chilled water to existing cooling coils within two single-zone AHUs providing space comfort for other non-sports related functions when the facility would ordinarily remain empty.

Each of these three scenarios requires design engineering beginning in the building program phase of a project and long before the contract document phase of the job. Each of these scenarios also requires O&M considerations because it takes more than just hitting a switch to turn on the temporary HVAC. At the same time, the changeover must be as simple as possible because many of these scenarios require an almost immediate response once the temporary equipment arrives on site. The building system(s) can’t require a one-week start-up and commissioning of the temporary equipment, so the tie-in, start-up, and operation must be simple.



Other more conventional temporary HVAC applications are:

  • Construction sites — Industrial and manufacturing — Pharmaceutical — Education institutions — Commercial and office space — Server rooms— Events and function facilities — Restoration and remediation — Emergency response


Rental equipment available for the HVAC industry include a wide range of sizes, types of equipment, and energy sources for the following applications:

  • Heating — Process heating — Heat rejection — Air conditioning — Process cooling — Spot cooling — Humidification —Dehumidification  — Air filtering — High pressure blower — Air scrubbers — Radiant heaters



While design engineers and architects may not initiate a discussion on temporary HVAC concepts, there are financial benefits to temporary equipment/systems being included in a building program — based on the number of hours at peak climate conditions, limits on existing equipment capacity and/or standby needs, O&M annual budgets, special event opportunities during periods when a building may be vacant, and emergency needs/scenarios. 

There are opportunities to save first cost, building space, and annual operation costs if the design team takes the time to think outside the box for a possible better way to a better product. ES






Note: Some information provided by Stefani Soucy, Marketing Manager, American Spot Cooling. The company provides temporary cooling, heating, dehumidification, and power solutions for power and HVAC rental needs with customized solutions to fit specific needs and environment. Also visit Risk Management Series Design Guidance for Shelters and Safe Rooms at