Would it be correct to include both of these in the award, or is there a more correct method to include this wage rate?
You appear to be applying the wage determinations correctly. You can use mix wage determination clauses in one contract when appropriate. FAR 36.101(c) states:
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(c) A contract for both construction and supplies or services shall include --
(1) Clauses applicable to the predominant part of the work (see Subpart 22.4), or
(2) If the contract is divided into parts, the clauses applicable to each portion.
It would be proper to apply construction clauses to the building alteration part and services clauses to the HVAC installation part. Also note that the terms "Davis-Bacon" and Service Contract Act" are now obsolete and have been replaced by the Wage Rate Requirements (Construction) statute and Service Contract Labor Standards statute, respectively.