機電工程數量計算方法之案例探討

Abstract

工程成本估算的基本概念為單價乘以數量，單價與數量這兩項發生估算錯誤時，對成本都會造成影響，其中數量計算發生錯誤之情形，極為頻繁。目前數量計算多著重於土建部分，對機電工程之數量計算較為忽略，然而機電工程約佔總工程造價之15%~30%，若有估算錯誤，影響亦甚鉅。為利釐清與歸納機電工程數量計算之方法，本研究包括三個部份：(1)機電工程之分類、(2)機電工程數量計算之原則與流程，以及(3)案例分析。 在機電工程分類方面，本研究依照機電工程不同的三種屬性，分別分類探討。第一，若依系統特性，可分為為機械系統及電氣系統等兩類，再依照系統功能，可向下細分各種子系統。第二，若依管線之傳輸物質，機電工程可區分為電能系統、液體系統及複合系統等3種類型，再依照系統功能向下細分各種子系統。第三，若依計算單位，可分類為單位計算及比例計算等2類。在此部分之探討，本研究亦分析影響數量計算的重要因素(稱為計算關鍵)。 在機電工程數量計算之原則與流程方面，本研究分析機電工程在實務上採用之數量計算方式，並依據傳輸物質分類，探討各類型系統之組成設備、管線。再就此進行實務經驗之彙整，針對不同機電工程之系統，分別探討各類別所需計算之項目及其計算單位，此部分可歸納出機電工程數量計算項目，可分為設備、管線與風管三類，計算單位分別為點數、長度與面積。 在案例分析方面，透過本研究提出的機電工程數量計算方式，進行案例分析。分析結果顯示，除本研究所提之計算原則與流程，應屬可行，所整理之計算關鍵應可協助工程人員理解機電工程之數量計算。

Estimating construction costs is related to the unit cost and quantity for each cost item. That is, accurately conducting quantity takeoffs (QTO) is crucial to generate acceptable cost estimates. Current practice pays much attention to the QTO of Civil/Structure/ architectural (CSA) construction part of a construction project. However, the Mechanical/Electrical/Plumbing (MEP) part could be approximately 15% to 30% of the total costs for of a construction project. To improve better understanding of the quantity takeoffs method for MEP construction, the study investigates three aspects, including the classification methods of MEP, the MEP takeoffs process and principles, and case study. Regarding the classification methods of MEP, three conclusions are derived. First, based on system characteristics, the MEP can be classified as mechanical systems and electrical systems. And they can be further sub-categorized according to system functions. Second, base on piping line transmission substance, the MEP can be divided into electrical energy systems, liquid systems, and composite systems. Again, they can be further sub-categorized according to system functions. Third, “units” are “ratios” are the two methods to conduct QTO. Regarding the MEP takeoffs process and principles, this study analyzes transmission substance categories and discusses the component of equipment and pipeline. This work integrates practical experience to discuss every category takeoffs method. Additionally, the cost items that can be categorized for QTO for MEP are equipment, piping line and duct. The quantity takeoffs units are identified to be point, length, and area. Regarding the case study, this study applies the MEP takeoffs process and principles to a case project. The results show that the proposed process and principles are feasible. Finally, the factors affecting QTO that are identified in this study should help inexperienced engineers to understand the takeoffs for MEP projects.