滿 亮 張小松 劉 劍 徐國英

(東南大學(xué)能源與環(huán)境學(xué)院 能源熱轉(zhuǎn)換及其過程測控教育部重點實驗室 南京 210096)

滿 亮 張小松 劉 劍 徐國英

(東南大學(xué)能源與環(huán)境學(xué)院 能源熱轉(zhuǎn)換及其過程測控教育部重點實驗室 南京 210096)

隨著我國經(jīng)濟(jì)的發(fā)展，建筑能耗在全國總能耗中所占的比例不斷增大。統(tǒng)計表明，暖通空調(diào)系統(tǒng)能耗占建筑總能耗55%[1]，因此對暖通空調(diào)系統(tǒng)進(jìn)行節(jié)能改造十分重要。為了降低暖通空調(diào)系統(tǒng)能耗，國內(nèi)外學(xué)者對冷水機組進(jìn)行了大量研究，其中溫濕度獨立控制系統(tǒng)因其節(jié)能、衛(wèi)生等特點被廣泛關(guān)注[2-3]。目前，溫濕度獨立控制主要通過固體吸附除濕或溶液吸收除濕等方法排出室內(nèi)濕負(fù)荷實現(xiàn)濕度控制，通過冷水機組制取高溫冷凍水排出室內(nèi)熱負(fù)荷實現(xiàn)溫度控制，研究表明具有良好的節(jié)能效果[4-5]。但固體吸附除濕存在設(shè)備體積大、需要較高的再生熱源溫度(140 ℃以上)等問題[6]，溶液吸收除濕存在溶液對管道腐蝕，除濕效率低等問題[7]。因此，國內(nèi)一些學(xué)者提出通過制取高低溫冷凍水的方式實現(xiàn)溫濕度獨立控制。梁彩華等[8]通過兩套以R22為工質(zhì)的冷水機組來制取兩種溫度的冷凍水(7 ℃和16 ℃)，用于空調(diào)負(fù)荷的熱濕分段處理。研究表明：當(dāng)表冷器設(shè)計溫差為7 ℃、出風(fēng)溫度為16 ℃時，冷水機組的COP相對于傳統(tǒng)空調(diào)方式提高9.14%，在回風(fēng)干球溫度為25 ℃、濕球溫度為21 ℃時，冷水機組COP提高達(dá)8%以上。但采用兩套機組存在造價高、耗材量大的問題。劉劍等[9-10]利用非共沸混合工質(zhì)的特性[11]，提出一種以大滑移溫度非共沸工質(zhì)R32/R236fa為循環(huán)工質(zhì)的新型雙冷源制冷機組，通過該冷水機組可制取不同溫度的高低溫冷凍水，從而實現(xiàn)溫濕度獨立處理。研究表明當(dāng)冷卻水進(jìn)水溫度為32 ℃，高、低溫冷凍水的出水溫度分別為18 ℃和7 ℃，R32質(zhì)量組分比例為60%時，機組COP可達(dá)3.92，可見該雙冷源制冷機組具有一定的節(jié)能潛力，對該系統(tǒng)的進(jìn)一步分析和優(yōu)化具有重要意義。

1 構(gòu)建雙冷源制冷機組分析模型

(1)

I=exq-Δexh-Ws

(2)

exh=h-h0-T0(s-s0)

(3)

(4)

1.1建立系統(tǒng)模型

圖1所示為采用混合工質(zhì)R32/R236fa的雙冷源制冷機組的系統(tǒng)流程圖，與之相對應(yīng)的理論循環(huán)T-s圖見圖2。該制冷循環(huán)由壓縮過程(1-2)、等壓冷凝過程(2-3)、節(jié)流過程(3-4，節(jié)流前后焓值相等，但非等焓過程)、等壓蒸發(fā)過程(4-5)和等壓蒸發(fā)過程(5-1)組成。

圖1 雙冷源制冷機組原理圖Fig.1 Schematic diagram of double cooling source refrigerating unit

圖2 制冷劑理論循環(huán)T-s圖Fig.2 T-s diagram of the theoretical cycle

mrexh1+Wcom=mrexh2+Lcom

(5)

Lcom=mrexh1+Wcom-mrexh2

(6)

mw,evalexh7+mrexh4=mw,evalexh6+mrexh5+Leval

(7)

Leval=mw,eval(exh7-exh6)-mr(exh5-exh4)

(8)

mw,evahexh9+mrexh5=mw,evahexh8+mrexh1+Levah

(9)

Levah=mw,evah(exh9-exh8)-mr(exh1-exh5)

(10)

mw,conexh10+mrexh2=mw,conexh11+mrexh3+Lcon

(11)

Lcon=mw,con(exh10-exh11)-mr(exh3-exh2)

(12)

mrexh3=mrexh4+Ltxv

(13)

Ltxv=mr(exh3-exh4)

(14)

Lsys=Leval+Levah+Lcon+Ltxv+Lcom

(15)

2 雙冷源制冷機組實驗研究

2.1 實驗裝置

基于大滑移溫度非共沸工質(zhì)R32/R236fa的單級壓縮水冷式雙冷源制冷機組實驗平臺，由雙冷源制冷機組裝置和測量裝置兩部分構(gòu)成，其中雙冷源制冷機組循環(huán)由制冷劑循環(huán)和水(冷凍水與冷卻水)循環(huán)組成。此外，雙冷源制冷機組裝置采用兩個蒸發(fā)器將蒸發(fā)過程分為兩段進(jìn)行，利用溫度不同的兩個冷源獲得高低溫度冷凍水。具體情況如表1和表2所示。

表1 雙冷源制冷機組裝置

表2 測量裝置

根據(jù)圖2和圖3可以判斷制冷循環(huán)和冷凍水循環(huán)的大致流程。制冷循環(huán)：大滑移溫度非共沸工質(zhì)R32/R236fa先經(jīng)壓縮機壓縮成高溫高壓的過熱氣體，再經(jīng)冷凝器冷凝成高壓過冷液體，高壓過冷制冷劑液體流經(jīng)儲液器、干燥過濾器后，經(jīng)電子膨脹閥節(jié)流到低溫低壓的兩相區(qū)，然后混合工質(zhì)先在低溫蒸發(fā)器內(nèi)蒸發(fā)，制取低溫冷凍水，再經(jīng)過高溫蒸發(fā)器蒸發(fā)，制取高溫冷凍水，蒸發(fā)后的工質(zhì)由壓縮機吸入，完成制冷循環(huán)。冷凍水循環(huán)：低溫蒸發(fā)器所制取的冷凍水通過循環(huán)水泵排入低溫冷凍水箱，之后經(jīng)過電熱器加熱，消耗冷量。高溫蒸發(fā)器制冷的冷凍水采用同樣方式抵消冷量。通過控制電熱器加熱量，改變高低溫蒸發(fā)器入口處高低溫冷凍水的溫度，可得實驗所需的高低溫冷凍水出水溫度。在冷凝器中進(jìn)行換熱之后的高溫冷卻水，進(jìn)入冷卻水水箱與自來水補水混合，之后通過電加熱器，將冷卻水溫度準(zhǔn)確控制到32 ℃，之后再進(jìn)入冷凝器，完成循環(huán)。

圖3 雙冷源制冷機組實驗裝置圖Fig.3 Schematic diagram of experimental system

2.2 非共沸工質(zhì)[18]

實驗中采用質(zhì)量比為60%/40%的R32/R236fa的混合工質(zhì)作為制冷劑。R32與R236fa均屬于環(huán)境友好型制冷劑，ODP均為0，GWP分別為650和6 300。

3 雙冷源制冷機組分析

對不同常用高低溫冷凍水組合進(jìn)行變工況實驗，具體運行工況如表3所示。

表3 變冷凍水溫度運行工況表

為便于理論分析計算，做出如下假設(shè)：1)冷凝器與蒸發(fā)器出口工質(zhì)為飽和狀態(tài)；2)忽略混合工質(zhì)在系統(tǒng)中的阻力；3)不計系統(tǒng)與環(huán)境間的散熱；4)壓縮過程絕熱但不等熵，等熵效率取0.65；5)忽略潤滑油對混合工質(zhì)熱物性的影響；6)蒸發(fā)器與冷凝器中最小傳熱溫差取5 ℃。

3.3 實驗結(jié)果與討論

圖4 雙冷源制冷機組變工況條件下各部件的理論損Fig.4 Theoretical exergy loss of all parts in variable chilled water temperature

圖5 雙冷源制冷機組變工況條件下各部件的實驗損Fig.5 Experimental exergy loss of all parts in variable chilled water temperature

表4 雙冷源制冷機組系統(tǒng)變工況條件下的總損

圖6 雙冷源制冷機組系統(tǒng)高低溫冷凍水溫度17 ℃/8 ℃條件下各部件的損Fig.6 Exergy loss rate of all parts in 17 ℃/8 ℃

4 結(jié)論

符號說明

COP——制冷效率

GWP——全球變暖潛能值

ODP——臭氧層消耗能值

T——溫度，℃

p——壓力，MPa

W——壓縮機功耗，kW

G——換熱介質(zhì)體積流量(水)，m3/h

m——質(zhì)量流量，kg/s

Q——制冷量，kW

下標(biāo)

com——壓縮機

r——制冷劑

con——冷凝器

sys——系統(tǒng)

eval——低溫蒸發(fā)器

txv——節(jié)流閥

evah——高溫蒸發(fā)器

w——水

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About the corresponding author

Zhang Xiaosong, male, professor, School of Energy and Environment, Southeast University, +86 13951974528，E-mail: rachpe@seu.edu.cn. Research fields: new technology of refrigeration and performance optimization of air conditioning system．

Exergy Analysis of Double Cooling Source Refrigerating Unit Based on Large Temperature Glide Zeotropic Mixture

Man Liang Zhang Xiaosong Liu Jian Xu Guoying

(School of Energy and Environment, Ministry of Education of Key Laboratory of Energy Thermal Conversion and Control, Southeast University, Nanjing, 210096, China)

To study the influence of the temperature of chilled water on the exergy loss of the double cooling source refrigerating unit, the model of exergy analysis on the unit that adopts the large temperature glide zeotropic mixture R32/R236fa (60%/40%) as refrigerant is established, and the experimental platform of the double cooling source refrigerating unit was set up for experimental exergy analysis in this paper. The theoretical exergy loss and the experimental exergy loss of the refrigeration unit are studied when the condensation temperature is 32 ℃ and the temperature of chilled water is 18 ℃/8 ℃, 17 ℃/6 ℃, and so on respectively. The results show that the minimum exergy destruction occurs when the inlet water temperature of the condenser is 32 ℃, higher and lower outlet water temperatures of the evaporator are 8 ℃ and 17 ℃. At the same time, the maximum exergy loss of the unit is compressor, followed by the condenser.

zeotrope; chiller; test conditions; exergy analysis

0253- 4339(2017) 02- 0089- 07

10.3969/j.issn.0253- 4339.2017.02.089

國家重點研發(fā)計劃項目(2016YFC0700303)和國家自然科學(xué)基金(51376044)資助項目。(The project was supported by the China National Key R&D Program (No. 2016YFC0700303) and the National Natural Science Foundation of China (No. 51376044).)

2016年4月21日

TB61+2;TU831.4

A

張小松，男，教授，東南大學(xué)能源與環(huán)境學(xué)院，13951974528，E-mail: rachpe@seu.edu.cn。研究方向: 制冷新技術(shù)與制冷空調(diào)系統(tǒng)性能優(yōu)化。