光伏-環(huán)路熱管/熱泵熱水系統(tǒng)在不同氣候區(qū)性能對比與優(yōu)化

李 洪，王美芳，張 曼

光伏-環(huán)路熱管/熱泵熱水系統(tǒng)在不同氣候區(qū)性能對比與優(yōu)化

李 洪，王美芳，張 曼

（燕山大學(xué)建筑工程與力學(xué)學(xué)院，秦皇島 066004）

為改善傳統(tǒng)太陽能光伏/光熱熱水系統(tǒng)運(yùn)行性能，拓展空氣源熱泵熱水系統(tǒng)應(yīng)用范圍，該文針對一種太陽能光伏-環(huán)路熱管/熱泵熱水系統(tǒng)開展了其在3種不同氣候區(qū)運(yùn)行性能對比及優(yōu)化研究。分別選擇北京、上海和廣州作為寒冷、夏熱冬冷和夏熱冬暖地區(qū)典型氣候代表城市，依據(jù)所建數(shù)學(xué)模型，模擬比對系統(tǒng)在3個(gè)地區(qū)的全年運(yùn)行性能，分析了集熱/蒸發(fā)器的朝向與安裝傾角對系統(tǒng)運(yùn)行性能的影響，并對其進(jìn)行了優(yōu)化；以傳統(tǒng)空氣源熱泵熱水系統(tǒng)為基準(zhǔn)，采用全壽命周期成本計(jì)算方法分析了系統(tǒng)的經(jīng)濟(jì)可行性。結(jié)果表明，相同安裝傾角正南朝向時(shí)，系統(tǒng)在廣州的太陽能綜合利用效率最高、節(jié)能性最佳；各地區(qū)理想安裝傾角下，北京和上海正南朝向時(shí)系統(tǒng)節(jié)能效益最優(yōu)，廣州則南偏東30°時(shí)節(jié)能率最高；與傳統(tǒng)空氣源熱泵熱水系統(tǒng)相比，系統(tǒng)在北京、上海、廣州的全壽命周期成本分別降低了58.75%、49.83%及53.09%，經(jīng)濟(jì)效益顯著。

太陽能；熱泵；效率；氣候條件；運(yùn)行性能

0 引 言

傳統(tǒng)化石能源的應(yīng)用促進(jìn)了經(jīng)濟(jì)的增長和生產(chǎn)力水平的提高，但同時(shí)導(dǎo)致能源危機(jī)以及環(huán)境污染問題日益嚴(yán)重[1-2]。因此，太陽能作為一種可持續(xù)清潔能源，受到越來越廣泛地推廣應(yīng)用。太陽能光伏光熱（photovoltaic and thermal，PV/T）技術(shù)一直是太陽能研究領(lǐng)域中備受關(guān)注的方向之一，以其良好的節(jié)能性、環(huán)境友好性等優(yōu)勢引起眾多學(xué)者的研究興趣[3-4]。目前所涉及的研究內(nèi)容主要包括設(shè)計(jì)更加高效的系統(tǒng)形式[5-6]、研究分析系統(tǒng)的經(jīng)濟(jì)性與可行性等[7]；研究方法包含數(shù)值模擬[8-10]、搭建試驗(yàn)臺進(jìn)行試驗(yàn)研究等[11-13]。通過學(xué)者們的不斷探索和研究，太陽能PV/T技術(shù)日臻完善。

環(huán)路熱管（loop heat pipe，LHP）是一種高效的兩相傳熱設(shè)備，具有優(yōu)良的傳熱性能與結(jié)構(gòu)特性，能夠在小溫差、長距離的情況下傳遞大量熱量，同時(shí)具有良好防凍性能，基于以上特性，部分學(xué)者提出將PV/T技術(shù)與LHP相結(jié)合的供熱系統(tǒng)[14-16]。研究表明，該類系統(tǒng)能夠提升太陽能光熱效率與光電效率，具有良好的光電光熱綜合利用性能[17-20]。此外，Zhang等[21-22]將PV/T集熱/蒸發(fā)器、環(huán)路熱管以及熱泵技術(shù)相結(jié)合，通過環(huán)路熱管與熱泵循環(huán)串聯(lián)連接的方式進(jìn)一步提升太陽能光熱轉(zhuǎn)換效率。張龍燦等[23]及Li等[24-25]則通過環(huán)路熱管與熱泵環(huán)路并聯(lián)的方式，實(shí)現(xiàn)多模式相互切換的太陽能環(huán)路熱管熱泵熱水系統(tǒng)，以更高效地滿足建筑生活用水需求。本課題組所提系統(tǒng)將太陽能PV/T技術(shù)與環(huán)路熱管及太陽能/空氣源熱泵相結(jié)合，不僅繼承了太陽能熱泵的優(yōu)點(diǎn)，同時(shí)解決了熱泵運(yùn)行所需部分電力，減少了能量的輸送環(huán)節(jié)，提高了太陽能綜合利用效率及其節(jié)能效益[25]。相關(guān)研究表明，太陽能PV/T系統(tǒng)及其與熱泵相結(jié)合的復(fù)合系統(tǒng)運(yùn)行性能受氣候條件、設(shè)計(jì)參數(shù)及安裝位置等因素影響顯著[26-30]。因此，在前期研究的基礎(chǔ)上，本課題組將針對文獻(xiàn)[25]中所研究系統(tǒng)，進(jìn)一步分析比對其在不同氣候區(qū)的運(yùn)行性能及變化規(guī)律，同時(shí)研究分析太陽能PV/T集熱/蒸發(fā)器的安裝傾角和朝向?qū)ο到y(tǒng)運(yùn)行性能及其經(jīng)濟(jì)性的影響。

1 系統(tǒng)描述

光伏-環(huán)路熱管/熱泵熱水系統(tǒng)（圖1），主要包括光伏-環(huán)路熱管（PV-LHP）和熱泵2個(gè)環(huán)路。PV-LHP環(huán)路主要由PV-T集熱/蒸發(fā)器和垂直螺旋管沉浸式冷凝器組成，水箱容積為150 L。熱泵環(huán)路中蒸發(fā)器采用無玻璃蓋板平直翅片平板式太陽能集熱器，冷凝器與熱管環(huán)路共用；壓縮機(jī)采用滾動(dòng)轉(zhuǎn)子式。開啟閥門1和2，關(guān)閉閥門3和4，系統(tǒng)在PV-LHP模式下運(yùn)行，PV/T集熱/蒸發(fā)器吸熱管中液態(tài)工質(zhì)吸收太陽熱能并蒸發(fā)為汽態(tài)工質(zhì)，汽態(tài)工質(zhì)沿蒸汽上升管到達(dá)冷凝器，在冷凝器內(nèi)冷凝液化將熱量傳給水箱中的冷卻水，液態(tài)工質(zhì)在重力作用下，沿凝液下降管回到PV/T集熱/蒸發(fā)器，完成一次循環(huán)。同時(shí)，集熱/蒸發(fā)器表面間隔鋪設(shè)的光伏板接收一部分短波輻射轉(zhuǎn)化為電能。關(guān)閉閥門1和2，開啟閥門3和4，系統(tǒng)則以熱泵模式運(yùn)行。系統(tǒng)主要設(shè)備結(jié)構(gòu)參數(shù)見文獻(xiàn)[25]。

圖1 光伏-環(huán)路熱管/熱泵熱水系統(tǒng)原理圖

用戶需求水溫設(shè)定為45 ℃，系統(tǒng)優(yōu)先以PV-LHP模式運(yùn)行，考慮到熱管啟動(dòng)負(fù)荷需求，并達(dá)到最大程度利用太陽能、節(jié)約傳統(tǒng)能源的目的，其運(yùn)行時(shí)段設(shè)定為8:00—14:00。該運(yùn)行模式結(jié)束后若水溫不達(dá)標(biāo)，則啟動(dòng)熱泵模式繼續(xù)加熱。

2 性能模擬與結(jié)果分析

根據(jù)能量守恒及熱力學(xué)第一定律，分別建立了PV-LHP和熱泵環(huán)路模型，PV-LHP模型主要包括PV/T集熱/蒸發(fā)器和冷凝器模型，其中PV/T集熱/蒸發(fā)器模型主要包括太陽能集熱模型，各結(jié)構(gòu)層及部件的能量平衡方程，冷凝器模型則由熱管冷凝段和冷卻水的能量平衡方程組成。為了簡化該復(fù)合系統(tǒng)的模擬計(jì)算，熱泵環(huán)路采用了經(jīng)驗(yàn)擬合模型[25]，模型中重點(diǎn)考慮了室外空氣溫度、冷凝器端入口水溫及太陽輻射照度3個(gè)主要因素的影響?；谠囼?yàn)測試數(shù)據(jù)，驗(yàn)證了所建模型的準(zhǔn)確性[25]。

基于所建系統(tǒng)模型，本文模擬分析了相同安裝傾角和朝向下系統(tǒng)在不同氣候區(qū)的運(yùn)行性能，進(jìn)一步分析比對了安裝傾角與朝向?qū)ζ涔?jié)能性、經(jīng)濟(jì)性的影響，并對其進(jìn)行了優(yōu)化，為該系統(tǒng)的實(shí)際工程應(yīng)用提供參考。

本文選取北京（40N°，116°E）、上海（31N°，121°E）、廣州（23N°，113°E）為寒冷、夏熱冬冷以及夏熱冬暖地區(qū)的代表城市。氣象參數(shù)統(tǒng)一引用Trnsys軟件中3個(gè)城市的典型氣象年參數(shù)，模擬中設(shè)定水箱初始水溫相同，春秋過渡季水箱初始水溫15 ℃，夏、冬兩季分別取20、5 ℃。

2.1 氣象條件分析

3座城市月平均空氣溫度及太陽輻射照度如圖2所示。廣州地區(qū)月平均空氣溫度明顯高于其余兩地，北京、上海、廣州月平均空氣溫度分別在270.61～300.95、278.21～302.27及288.07～303.37 K范圍內(nèi)浮動(dòng)，3個(gè)地區(qū)典型年最高月平均太陽輻射照度分別為544.2、499.5和529.1 W/m2，最小值分別為334.7、271.9、243.7 W/m2。

2.2 相同安裝傾角和朝向

為了明確氣象條件對系統(tǒng)運(yùn)行性能的影響，擬采用相同安裝傾角（35°）和朝向（正南）模擬分析系統(tǒng)在3個(gè)地區(qū)的全年運(yùn)行性能變化規(guī)律。

圖2 月平均空氣溫度及太陽輻射照度

圖3顯示的是系統(tǒng)在3個(gè)地區(qū)的月均太陽能供熱百分比和凈耗電量。可以得出，系統(tǒng)在北京、上海、廣州的年均凈耗電量分別是229.85、233.01和128.94 kWh，年均太陽能供熱百分比分別是57.42%、53.35%、58.45%。系統(tǒng)在廣州凈耗電量比北京、上海分別減少43.9%、44.7%。這是由于廣州地處夏熱冬暖地區(qū)，該氣候區(qū)的氣溫年較差和日較差均小，太陽輻射照度較高，這種氣象條件更有利于系統(tǒng)2種模式的運(yùn)行。模擬結(jié)果顯示，相比北京、上海，系統(tǒng)在廣州的年均光電效率略低，年均光熱效率則高出8.33%和5.72%，年均光電光熱綜合效率分別高出8.19%和5.58%。從太陽能光電光熱綜合利用的角度出發(fā)，系統(tǒng)在廣州適用性最強(qiáng)，其次是上海、北京。

圖3 月均凈耗電量與太陽能供熱百分比

2.3 安裝傾角與朝向的優(yōu)化

對于固定式安裝的PV/T集熱/蒸發(fā)器，其安裝傾角與朝向?qū)ο到y(tǒng)光電光熱性能影響較大，而理想的安裝傾角與朝向隨氣候條件變化顯著。因此，有必要針對系統(tǒng)的安裝傾角與朝向進(jìn)行優(yōu)化，以進(jìn)一步確保系統(tǒng)在各氣候區(qū)運(yùn)行的可靠性。

首先，基于緯度修正法，確定安裝傾角的變化范圍，北京選取35°、40°、45°、52°，上海選取25°、30°、35°、40°，廣州則以18°、23°、28°、33°為代表?；谏鲜霾煌瑑A角，模擬計(jì)算了集熱器表面月平均輻射量、系統(tǒng)的發(fā)電量和集熱量，計(jì)算結(jié)果顯示：系統(tǒng)的集熱量與發(fā)電量變化趨勢與月平均輻射量保持一致。以集熱器表面接收更多輻射量為目標(biāo)，初步選定3個(gè)地區(qū)的較優(yōu)安裝傾角，北京為35°、52°，上海為35°、25°，廣州則是35°、20°。基于此，進(jìn)一步模擬分析了系統(tǒng)在3種地區(qū)運(yùn)行性能隨安裝傾角的變化情況，結(jié)果如表1所示。以太陽能供熱百分比最大為目標(biāo)，最終選定系統(tǒng)在北京、上海、廣州的理想安裝傾角分別為35°、25°、35°。

表1 不同安裝傾角下系統(tǒng)的運(yùn)行性能對比

基于最優(yōu)安裝傾角，進(jìn)一步模擬計(jì)算了系統(tǒng)運(yùn)行性能隨方位角的變化規(guī)律，考慮的朝向有?45°、?30°（南偏東為負(fù)），0°（正南），30°、45°（南偏西為正），結(jié)果如表2所示。由結(jié)果可以得出，在北京，PV/T集熱/蒸發(fā)器朝正南方向安裝時(shí)，年太陽能供熱百分比最高，達(dá)57.42%；年凈耗電量最低，與其他朝向相比依次減少12.9%、6.4%、8.3%及18.0%。在上海，PV/T集熱/蒸發(fā)器朝正南方向安裝時(shí)，年凈耗電量和太陽能供熱百分比最佳，與南偏西45°相差最大，與其余朝向相比，略有優(yōu)勢。在廣州，則朝向?30°安裝時(shí)性能最優(yōu)，與0°和?45° 2個(gè)朝向相差不多，與南偏西的2個(gè)系統(tǒng)相比，節(jié)能率分別提升10.1%和16.15%。

表2 年凈耗電量和太陽能供熱百分比

注：0°表示正南。

Note: 0° represents the south.

綜上可得，在不同氣候條件下，安裝傾角和朝向不同，對系統(tǒng)性能影響程度也不同。在所推薦的理想安裝傾角和朝向下，北京、廣州兩地的節(jié)能效果較優(yōu)，太陽能供熱百分比分別為57.42%和58.45%，上海稍低為53.82%。

3 經(jīng)濟(jì)效益分析

基于上述性能模擬分析結(jié)果，進(jìn)一步采用全壽命周期成本（life cycle cost，LCC）分析方法評估優(yōu)化后的系統(tǒng)在不同氣候區(qū)應(yīng)用的經(jīng)濟(jì)可行性。LCC由初投資費(fèi)用與運(yùn)行、維護(hù)費(fèi)用組成，系統(tǒng)的現(xiàn)值可由下式計(jì)算

式中為系統(tǒng)的現(xiàn)值，元；為系統(tǒng)第一年運(yùn)行維護(hù)費(fèi)用，元；為折現(xiàn)率；為壽命周期。

系統(tǒng)初投資根據(jù)各部件在當(dāng)?shù)氐钠骄鶅r(jià)格取值，系統(tǒng)第一年的維修費(fèi)用按初投資的2%計(jì)算，運(yùn)行和維護(hù)費(fèi)用的通貨膨脹率和折現(xiàn)率分別為2%和5%，設(shè)定系統(tǒng)的發(fā)電量采用“全額上網(wǎng)”模式提供給國家電網(wǎng)，并將獲取發(fā)電補(bǔ)貼考慮到系統(tǒng)運(yùn)行費(fèi)用中，計(jì)算結(jié)果列于表3、表4?？梢钥闯?，所研究系統(tǒng)的初投資是傳統(tǒng)空氣源熱泵系統(tǒng)的2.5倍。但是，由于其年耗電量只有空氣源熱泵系統(tǒng)的一半左右，并且系統(tǒng)的年發(fā)電量占其耗電量的一半以上，北京、上海、廣州的太陽能供電比例分別為53%、51%和66%，因此，整個(gè)壽命周期內(nèi)，與傳統(tǒng)空氣源熱泵系統(tǒng)相比，該系統(tǒng)運(yùn)行維護(hù)費(fèi)用降幅明顯，北京、上海、廣州分別減少了67.86%、59.00%、62.21%，系統(tǒng)的LCC分別減少58.75%、49.83%及53.09%。綜上，雖然所研究系統(tǒng)初投資較高，但從全壽命周期來看，其運(yùn)行經(jīng)濟(jì)效果顯著。

表3 光伏-環(huán)路熱管/熱泵熱水系統(tǒng)的LCC分析

表4 空氣源熱泵熱水系統(tǒng)LCC分析

4 結(jié) 論

本文以太陽能光伏-環(huán)路熱管/熱泵熱水系統(tǒng)為研究對象，模擬分析了系統(tǒng)在3種不同氣候區(qū)的運(yùn)行性能，優(yōu)化了PV/T集熱/蒸發(fā)器的安裝傾角與朝向。在此基礎(chǔ)上，采用LCC分析方法評估了系統(tǒng)的經(jīng)濟(jì)效益。主要結(jié)論如下：

1）PV/T集熱/蒸發(fā)器按照相同安裝傾角和朝向設(shè)置時(shí)，系統(tǒng)在廣州的太陽能供熱百分比最高，達(dá)到58.45%，耗電量最少，節(jié)能效果最顯著。從太陽能光電光熱綜合利用的角度出發(fā)，系統(tǒng)在廣州適用性最強(qiáng)，其次是上海、北京。

2）不同氣候條件下，安裝傾角和朝向?qū)ο到y(tǒng)性能的影響程度不同，為提高系統(tǒng)的太陽能利用效率，應(yīng)對其安裝傾角和朝向進(jìn)行優(yōu)化。在理想的安裝傾角和朝向下，北京、廣州兩地的節(jié)能效果較優(yōu)，太陽能供熱百分比分別可達(dá)57.42%和58.45%，上海稍低，為53.82%。

3）與傳統(tǒng)空氣源熱泵系統(tǒng)相比，系統(tǒng)初投資顯著提高，但在整個(gè)壽命周期內(nèi)，系統(tǒng)的運(yùn)行維護(hù)費(fèi)用降幅明顯，LCC依次減少58.75%、49.83%及53.09%，經(jīng)濟(jì)效益顯著。

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Feasibility comparison and optimization on a loop-heat-pipe type PV/T heat pump water heating system in different climatic regions

Li Hong, Wang Meifang, Zhang Man

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In this paper, energy performance of a loop-heat-pipe (LHP) type solar photovoltaic/thermal (PV/T) heat pump water heating system is studied to evaluate its feasibility in three different climatic regions. A mathematic model of this system in our former study is built and validated using outdoor test data. On the basis of this model, influences of main structural design parameters including the installation angle and the orientation of the PV/T collector/evaporator are discussed and main parameters are optimized to further improve system operation performance. Based on optimal design parameters, economic feasibility of the proposed system under different weather conditions is analyzed using the life cycle cost (LCC) method. The system is integrated with solar PV/T, loop heat pipe and solar assisted air source heat pump technologies. This combined approach is benefit for improving solar energy comprehensive application efficiency of conventional solar PV/T systems. Moreover, it enlarges the application region of traditional air source heat pump water heating systems. Depending on different solar radiation conditions, this system can operate in different modes including solar photovoltaic LHP mode, solar assisted air source heat pump mode and the only air source heat pump mode. In this study, Beijing, Shanghai and Guangzhou were selected as typical representative cities in cold area, hot summer and cold winter area, hot summer and warm winter area. Typical meteorological year (TMY) data of three cities were extracted from TRNSYS. Based on TMY data, annual operation performance of the proposed system is calculated through the validated dynamic mathematic model. Firstly, PV/T collector/evaporators of three systems are all fixed in the south direction and the same installation angle (35°) was chosen. In this case, annual net power consumptions and solar heating fractions of three systems are calculated and compared. Then installation angles and orientations are optimized to ensure maximum solar energy application. The investigation results show that, among three cities, the solar heating fraction in Guangzhou is the largest. And the least electricity is consumed in Guangzhou, which is decreased by 43.9% and 44.7% respectively compared with those in Beijing and Shanghai. The comprehensive photothermal efficiency in Guangzhou is 8.19%, 5.58% higher than those in Beijing and Shanghai. Therefore, from the view of solar energy comprehensive efficient utilization, the application of the system is most proposed in Guangzhou, and then followed by Shanghai and Beijing. Considering impacts of installation angles and orientations, the ideal installation inclination of the system in Beijing, Shanghai and Guangzhou are 35°, 25°, and 35°, and the optimal installation directions of Beijing and Shanghai are facing the south, while that of Guangzhou is 30°east to the south. With the optimal parameters, it is found that solar heating fractions in Beijing and Guangzhou (i.e. 57.42% and 58.45%) are slightly higher than that in Shanghai. It is concluded that influences of two structural parameters are different for such system in different climatic areas. To ensure maximal solar energy application, it was necessary to optimize these two parameters. For the life cycle cost analysis, a traditional air source heat pump hot water heating system is chosen as the base system. The analysis results indicate that the initial investment of the system increases significantly, which is 2.5 times of that of the base system. However, the annual power consumption of the system is about half of that of the traditional system. Besides, solar power supply fractions in Beijing, Shanghai and Guangzhou are 53%, 51% and 66% respectively. As a result, the total operation and maintenance fees in the life cycle drop significantly, which are reduced by 67.86%, 59.00%, and 62.21% in Beijing, Shanghai and Guangzhou. The life cycle cost is correspondingly reduced by 58.75%, 49.83% and 53.09% in three cities. In conclusion, the application of this system is feasible for considered weather conditions in terms of both the operating performance and economic benefits.

solar energy; heat pump; efficiency; climatic conditions; operation performance

李 洪，王美芳，張 曼. 光伏-環(huán)路熱管/熱泵熱水系統(tǒng)在不同氣候區(qū)性能對比與優(yōu)化[J]. 農(nóng)業(yè)工程學(xué)報(bào)，2020，36(1)：252－256.doi：10.11975/j.issn.1002-6819.2020.01.030 http://www.tcsae.org

Li Hong, Wang Meifang, Zhang Man. Feasibility comparison and optimization on a loop-heat-pipe type PV/T heat pump water heating system in different climatic regions[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2020, 36(1): 252－256. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.2020.01.030 http://www.tcsae.org

2019-06-28

2019-08-26

河北省高等學(xué)?？茖W(xué)技術(shù)研究項(xiàng)目（ZD2018031）

李 洪，博士，副教授，研究方向?yàn)閺?fù)合熱源熱泵技術(shù)及太陽能光熱綜合利用技術(shù)。Email：be_leecandy@163.com

10.11975/j.issn.1002-6819.2020.01.030

TE0

A

1002-6819(2020)-01-0252-05